Humidifier, Dehumidifier, Purifier, Diffuser & Ionizer (Explained)

These home devices offer enhanced life quality by improving the air you breathe.

Indoor air does not benefit from outdoor ventilation levels and can sap your energy levels and aggravate respiratory illnesses.

Also, air conditioning and heating can dry out and crack your skin and furniture and make your house plants sad.

How can these devices help, and which are best for you and your family?

indoor air quality appliances and devices

What Are They?

All these devices change the air quality in your living space. Some, like the humidifier and dehumidifier, work in opposition to each other.

A humidifier puts moisture into the air, and a dehumidifier removes it.

An air purifier scrubs the air to remove pollutants, and a diffuser adds essential oils to your room air.

An ionizer adds negative ions to your room.

None of these devices class as medical devices for therapeutic purposes, but you typically benefit from breathing more easily, and they reduce allergen flare-ups.

A humidifier is often part of any medical device using therapeutic air to treat sleep apnea or other respiratory conditions.

How Do They Work?

Each device performs a different action, and they work as follows:


air humidifier

A humidifier puts moisture into the air and works in one of five different ways:

  • Central humidifiers – built-in as part of air conditioning or heating and add humidity to the whole house – most expensive type but most effective for producing a complete house solution.
  • Evaporators – a single unit system that uses a fan to blow moist air into a room.
  • Impeller Humidifiers – child-friendly as they create a cool mist dispersed into the air by high-speed rotating disks.
  • Steam vaporizers – inexpensive but carry the risk of burns. The unit uses electricity to heat water, cool the steam, and then dispense it into the air,
  • Ultrasonic humidifies – ultrasonic vibration creates a moist mist, either warm or cool.


air dehumidifier

A dehumidifier removes water vapor from the air and converts it into water droplets.

Most dehumidifiers work in one of two ways:

  • Using refrigeration coils to condense water (can be described as a compressor); or
  • Using absorbent materials to trap water (desiccant).

Air Purifier

air purifier

Air purifiers use a fan to draw air through a series of filters.

These filters (paper, fiber, or mesh) trap the dust, pollen, animal hair, and other particles suspended in your room air and allow cleaner air back into your room.

Some models include a UV filter to destroy some microscopic living organisms like bacteria and mold.

These are more expensive, cost more to operate, and are ineffective against UV-resistant bacteria.


essential oil diffuser

A diffuser operates using one of four different mechanisms:

  • Ultrasonic vibration – a vibrating plate mixes the essential oils with water and disperses them as a fine mist into the air. The absence of heat is beneficial for the oils (most oils change when heated) and safe to use around children (no risk of burns).
  • Heat – typically, these use a candle to heat the water and oil mixture to create vapor.
  • Evaporation – fan passes air over a pad or wick containing the oil; air movement encourages oil molecules to lift from the material and into the room.
  • Spray or nebulizer – the action is like a scent spray – a concentrated mist disperses into the room. A timer can control the frequency of operation, and some devices using a nebulizer are motion activated.


An ionizer can be a standalone device or combined with an air purifier. An ionizer uses electricity (high voltage) to charge particles in the air (negative ions).

This process happens in nature near running water, which is why the air feels fresher and more invigorating near a fountain or waterfall.

In your home, it happens when you run a tap or have a shower.

The two different types of ionizers are:

  • Electrostatic precipitators – electrical discharge (corona discharge) blasts out a cloud of negative ions, and the resulting dust particles migrate to a positively charged plate.
  • Ion generators disperse negative ions but don’t use a collection plate, and the dust falls everywhere.

What are the Benefits and Risks?

Modern living and stagnant air within our houses do not create the best environments for your airways, eyes, hair, and skin.

Each of these devices aims to improve the air quality you experience in your home or office.

Humidifier Benefits

Your body – and in particular the parts involving respiration – need moisture. Dry air is painful air for most people.

However, too much humidity (over 60%) is not healthy, according to EPA guidelines.

The right amount of humidity (30-50%) promotes:

  • Reduced risk of influenza – research indicates humidity at 40% deactivates some viruses.
  • Turning a dry, painful cough into a productive one that removes phlegm from your body.
  • Lubricated airways and reduced snoring.
  • Healthy looking skin and hair – these need moisture to look healthy.
  • Warm feelings so you can turn down the heating.
  • Happy houseplants – most houseplants prefer moist air to dry.
  • Long-lived wooden and wicker furniture – these natural materials need some moisture.
  • Reduced static build-up.

These benefits mean humidifiers are helpful for the relief of:

  • Dry skin.
  • Sinus congestion and the associated headaches.
  • Dry throat.
  • Nose irritation.
  • Nosebleeds from dry irritation.
  • Cooling irritated vocal cords.
  • Dry coughs.
  • Cracked lips.
  • Hay fever symptoms.
  • Asthma and allergy flare-ups.

Humidifier Risks

The risks associated with humidifiers relate to:

  • Water quality.
  • Operational features.

If the water is dirty or contains mineral deposits (tap water), the water vapor coming out of the machine can contain harmful particles.

The best practice is to regularly change the water in the reservoir and use distilled or purified water. Plus, you need to follow the manufacturer’s recommended cleaning process.

Clean water is essential to avoid adding to your room pollution and bacterial load.

Operational risks include:

  • Running a humidifier with a dry reservoir – the machine can overheat, break down or catch fire.
  • Steam burns – some machines heat the water to create steam.
  • Producing dangerous levels of humidity above 60%.

You can avoid operational risks by using a humidifier that does not use steam (opt for a cool-mist type) and switches off when the reservoir is empty or the room reaches a target humidity level.

Dehumidifier Benefits

Some climates are too moist, and some areas in the home generate an excess of moisture – showers, gas central heating, and drying clothes can all result in an excess moisture load in the air in your home.

Too much humidity can result in increased:

  • Dust mites.
  • Mold and mildew.
  • Undesirable bacteria.

Removing the excess moisture using a dehumidifier can benefit you and your family by:

  • Reducing allergy symptoms (wheezing, sneezing, chest pain, eye irritation, itching) by reducing exposure to mold, dust mites, pollen, and dander.
  • Easing asthma flare-ups by allowing you to breathe lighter, less heavy air.
  • Cooling your home and reducing the need for air conditioning.
  • Reducing or eliminating mold and mildew growth.

Dehumidifier Risks

The risks of using a dehumidifier include:

  • Removing too much moisture from the air to dangerously low levels.
  • Overflowing water tank.
  • Motor overheating.
  • Throwing out dirty air.

Most modern dehumidifiers have automatic cut-off switches to prevent the motor from overheating, the water reservoir overflowing, and the machine continuing to operate if you knock it over.

The air exhaled into your room passes through a filter with an antibacterial coating. Regular replacement of the filter in line with the manufacturer’s recommendations ensures the air is clean and safe.

A dehumidifier cleans the air passing through it, but not to the same level as an air purifier.

Removing too much moisture from your room air can result in all the health issues associated with too dry air.

Regularly checking humidity levels with a hygrometer will ensure you maintain safe humidity levels in your home.

Air Purifier Benefits

No one wants to breathe dirty air, and pollution causes unnecessary deaths by causing and aggravating ill-health.

Indoor air (according to the EPA) is between two to five times more contaminated than outside air.

You can improve your indoor air quality by opening all the windows and doors and forcing an air change, but this is not always possible as part of your routine.

An air purifier cleans the air in your room, and this means:

  • Less cooking odors – air purifiers remove the smell of burnt food or fish as effectively as other large particles.
  • Removal of pet allergens – dander, hairs, and all the other allergy-inducing particles your pet puts into the air.
  • Removal of smoke particles – wood-burning stoves adds unwelcome and potentially harmful particles, not to mention the risks of secondary smoke damage from those family members or guests with a smoking habit.
  • Less dust – air always has dust; a significant portion of it is dead human skin cells. If you scrub this dirt from the air before it settles, you have cleaner furniture, and your electronics live longer.
  • Fewer bacteria, germs, and other allergens – a HEPA filter with a UV bulb will kill or remove almost all the harmful microorganisms leaving you with clinically clean air.
  • You and your family breathe more easily and have fewer respiratory issues.

Air Purifier Risks

The potential risks associated with your air purifier depend on how the model operates and how clean you keep the filters:

  • Ozone production.
  • Dirt.
  • Chemicals and odors.

More on these three risks.

Some air purifier models generate ozone to kill mold and bacteria. Industrial applications use high levels of ozone to purify air and water.

Still, these are not for domestic use (except by professional subcontractors) because high ozone levels are harmful to health.

The Center for Disease Control carefully regulates the use of ozone to protect worker health.

The amount of ozone generated by a domestic appliance is unlikely to be at sufficient levels to significantly harm you, but neither is it at levels to effectively resolve all issues with bacteria and odors.

The air purifier does not create dirt particles; the risk lies in how efficiently the air purifier deals with dirt.

Ionizers generate negative ions that encourage dirt particles to deposit from the air onto your furniture and carpet. If you don’t remove this dirt, then eventually, it returns to the air.

HEPA (High Efficiency Particulate Air) filters remove particles from the air – industry, and clinical settings approve these as the most efficient.

A HEPA filter will not deal with odor or VOCs (Volatile Organic Compounds) unless combined with an activated carbon filter – for safer air, you want both types of filters in your air purifier.

The filter works until it is clogged with dirt and loses its effectiveness.

To maintain clean air production, you must regularly replace your filters and keep your unit maintained.

An efficient air purifier with HEPA and activated charcoal filters is relatively risk-free if you routinely clean and maintain it and use it within the manufacturer’s operational guidelines.

Diffuser Benefits

A diffuser disperses aromatherapy oils into your air, these oils smell pleasant, and many people prefer specific oils that help them relax or have other potential benefits.

Potential benefits from using a diffuser include:

  • Relaxation – scent has a hotline to your brain, and some scents are relaxing, others energetic, and some simply make you feel good.
  • Calmness – relaxed people reduce muscle tension and breathe more deeply.
  • Focus – it may be an associated response, but some aromatherapy oils will help you work that little bit harder.
  • Mood-boosting -your home smells lovely, and you feel great.
  • Natural oils don’t add to the chemical burden in your air.
  • Reducing mold and bacteria – some oils (eucalyptus and tea tree oil) have antibacterial properties.
  • Reducing the symptoms of stuffy noses and colds.
  • Discouraging pests like mosquitos.
  • Promoting natural sleep.

The effectiveness of the diffuser depends on the selection of appropriate aromatherapy oil for your preferred outcome.

Diffuser Risks

Essential oils can be dangerous if you don’t use them appropriately.

Before diffusing any essential oil for aromatherapy or scenting your room, ensure you understand the properties of that oil.

Safe tips for oil diffusion are:

  • Diffuse in a well-ventilated room for no more than 30 minutes.
  • Make sure pets (especially cats) can exit the room.
  • Always dilute following guidelines – don’t add an extra drop or two as more is not better.
  • Check for individual sensitivity and reaction.
  • Consult a doctor if asthmatic.
  • Avoid when pregnant – no evidence for help or harm, but minimizing any potential risk doesn’t harm your baby.

The FDA considers some essential oils as generally safe for use – lavender and chamomile are typically safe for soothing babies (and adults) to sleep as a room fragrance.

Risks from the diffuser include:

  • Use of candles – a naked flame without supervision is a fire risk.
  • Plastic components may alter the essential oil adversely.
  • Leaving it running for excess time – use a timer or automatic shut-off.

The significant risk with diffusers lies with the quality and type of aromatherapy oil, especially for cats and dogs.

Ionizer Benefits

Many electrical devices generate an excess of positively charged particles, which can adversely impact your health.

Redressing the balance by injecting negatively charged ions into your room air links with:

  • Better mood – air with negative ions feels fresher.
  • Removal of dust and other pollutants.
  • Decrease in bacterial and viruses.
  • Reduced headaches and indoor sickness.
  • Better mental and physical performance.

Natural air contains a mixture of positive and negative ions.

Typical room air includes an excess of positive ions compared with outside air.

Negative ions are not a medical therapy, but many people report enhanced mood and energy by having more negative ions in their lives.

Ionizer Risks

The risks associated with ionizers depend on how the ionizer works because ozone production is undesirable as high levels (100 parts per million) are hazardous.

There is also some risk of increased production of VOCs and other harmful molecules.

None of these claims for and against ionizers operation have scientific research to give a definitive answer in either direction.

What Do You Need to Know?

If you are thinking about investing in one of these devices, what are the critical features to help you decide on the best option?


All humidifiers have a water tank and convert the water in the tank into water vapor to disperse into the room air.

The size of the water tank dictates the size of the humidifier unit.

Humidifiers range in size – from tiny (50 oz reservoirs) that can humidify a car to console models with a six-gallon reservoir that will humidify your entire house.

You want to fit your humidifier to the size of the room and how long it will run before you need to top up the reservoir.

Ultrasonic humidifiers are the quietest, but most have at least two running modes – low and high.

Some models are lower noise than others, and if you want to use a humidifier in your bedroom, then the lower levels of noise will give you a more restful night.

In a baby’s room, the fan’s noise can be comforting and promote sleep by providing a level of background noise that prevents the child from noticing household noises.

If there are children in your household, avoid humidifiers that generate steam to reduce the risk of accidents.

The crucial safety feature is an automatic cut-off when the reservoir is empty – avoid buying a humidifier without this feature.

Optional additional features include:

  • Built-in hygrometer – acts like a thermostat by monitoring humidity levels and switching off when you reach the desired percentage.
  • UV Light or tank coatings to kill bacteria.
  • Night light function – provides a comforting glow for children.
  • Aromatherapy oil dispenser to provide the benefits of a diffuser as well as a humidifier.

A central humidifier installation for your entire home can cost anything from $200 to $1,000 to install and a couple of hundred dollars a year to run.

Standalone, portable units vary from under $20 to $200.


A dehumidifier size depends on the amount of moisture it can remove from the air over 24 hours – anything from 0.1 to 6 gallons for domestic devices.

Industrial devices are louder, more expensive, and remove large water volumes because people hire them to cope with saturated walls and carpets after flooding.

Some construction companies use industrial dehumidifiers to speed up drying plaster.

Most domestic devices contain a water tank to collect the condensed water, and you need to empty it regularly.

Although a dehumidifier runs on electricity, the annual running cost is modest depending on usage – between $10 and $100.

The unit prices range from $100 to $300 for most models, but there are some smaller ones around $50.

Optional features include:

  • Wheels for easy mobility.
  • Humidity settings.
  • Hygrometer.
  • Low noise settings.
  • Automatic shut-off.
  • Automatic settings.
  • Protection against freezing.

Air Purifiers

Comparing different air purifiers involves examining various features; the essential ones are:

  • Specific pollutants – you may be more interested in particular classes of pollutants like pet hair or pollen and want a model that addresses that issue. If odor is an issue, you need an activated carbon filter as one of the filters included in the air purifier.
  • Clean air delivery rates (CADR) – high numbers mean more particles removed and larger rooms serviced. You need a high rating to remove dust mites.
  • HEPA filters – considered the best for removing the maximum quantity of allergens. Read the label carefully. “HEPA-like” is not the same as a genuine and efficient HEPA filter.
  • Noise levels – depends on the quality of the fan; a low Db rating indicates quieter operation.
  • Running costs – the significant running cost is the replacement of filters. Some are washable, but generally, you can expect to replace the filters at least once a year.

Optional or bonus features:

  • Indicator light for filter replacement – takes out the guesswork.
  • Programmable timer.
  • Remote control or app integration.

You can expect to pay between $40 a $200 for a domestic air purifier.


You can expect to pay between $20 and $200 for a diffuser, with the least expensive being simple manual evaporation diffusers and the more expensive electronic devices that give you additional features.

Potential extra features include:

  • LED lights – act as a night light and let you know when the machine is on.
  • Timers – if you can fragrance your room in an hour, then set the timer to run at a convenient time.
  • Automatic shutdown – when the reservoir is empty, the machine switches off.


Most ionizers come packaged with an air purifier as an additional feature.

You can buy a device that only generates negative ions for under $50.

Most people interested in this product also want air purification with ironizing thrown in as a bonus.

What Device is Best for You?

Your need for any of these devices depends on your family members’ health issues and where you live for humidity levels and pollutants.

Humidifier vs. Dehumidifier

Weighing the benefits of a humidifier vs. dehumidifier will not occupy much of your time. You either need to increase or decrease the humidity in your home.

The best way of determining the need for a humidifier vs. dehumidifier is to invest $10 in a hygrometer to measure your ambient humidity.

If your humidity levels are below 30%, you will benefit health-wise from adding some moisture to your air; if above 50%, then your family and home will be better with a dehumidifier.

It is possible to benefit from a dehumidifier and a humidifier – although running both simultaneously is pointless.

Running a dehumidifier in a bathroom prevents the water vapor from condensing on the walls.

Many apartments have enclosed bathrooms with no natural ventilation. A dehumidifier can minimize issues with damp.

Additionally, you may need humidity in a dry winter in a centrally heated house but want to remove humidity during a hot, wet summer.

The best approach is to monitor your humidity levels with the same approach as temperature for heating and cooling.

Humidifier vs. Air Purifier

A humidifier puts moisture into your room’s air, whereas an air purifier removes pollutants from the air.

These devices perform different functions, and you can run both to benefit your family.

You may want to clean your air for maximum effectiveness before adding humidity for a restful night’s sleep.

Humidifier vs. Diffuser

A diffuser adds aromatherapy oil molecules to your air and adds some water molecules as part of that process.

A diffuser does not add a significant amount of moisture to a room because that is not its primary function.

If you need to add moisture and want fragrance, opt for a humidifier combined with a diffuser to get both functions.

If you live in a climate or a home that needs moisture removal from the air, a standalone diffuser will not severely impact your moisture levels.

Humidifier vs. Ionizer

Humidifiers put water droplets into the air. Ionizers increase the number of negative ions in the air.

An ultrasonic humidifier can combine with an ionic filter, but this feature mainly kills bacteria and mold spores.

The benefits of a humidifier are separate and additional to the benefits of an ionizer.

Choose a humidifier if your room air contains less than 30% humidity, and you will improve your overall health. Choose an ionizer if you feel it benefits your mood and energy levels.

Dehumidifier vs. Air Purifier

Dehumidifiers condense water vapor and turn it into liquid water.

A dehumidifier has a slight cleaning effect on the air because water vapor associates with dirt particles, and the reservoir may collect some dirt from the air.

The removal of dirt and pollutants from the air is not the primary purpose of a dehumidifier, and it is inefficient at air purification.

An air purifier removes pollution from air – solid particles, and if there is an activated carbon filter odor. An air purifier does not reduce the humidity in a room.

Choose a dehumidifier if you need to reduce moisture and an air purifier to clean the air.

Dehumidifier vs. Diffuser

A diffuser adds scent and water droplets to the air, whereas a dehumidifier removes water droplets from the air.

You can use a diffuser to fragrance a room after removing the excess humidity without severely impacting the humidity levels.

Air Purifier vs. Ionizer

Some manufactures describe their ionizers as filterless air purifiers, and some air purifiers combine an ionizer with their other functions.

Ionizers help remove pollutants from the air.

The negative ions clump the positively charged particles into larger masses that fall to the ground onto your carpets and furniture as dust.

Air purifiers trap the dust and other pollutants on filters inside the machine.

An ionizer is erratic in its air cleaning effect because the purpose of an ionizer is to provide more negative ions. An air purifier will efficiently remove pollutants from your room air and give you and your family clean air to breathe.

Air Purifier vs. Diffuser

An air purifier removes particles and molecules from the air, where a diffuser adds aromatherapy oil molecules into the air.

Combining a diffuser with an air purifier lets you load the clean air with your preferred scent molecules. These two devices act in opposite ways – one removes and the other adds.

Diffuser vs. Ionizer

Both these devices add something to your room’s air.

The diffuser adds aromatherapy oil droplets, and the ionizer adds negative ions. Both actions act on your mood and energy levels.

The effect of a diffuser is instantaneous and allows you to fine-tune your benefits with a broad selection of different oils for different impacts.

The result of ionized air in the home is less studied, but many people benefit from enhanced positivity and energy.

Are These Devices Safe Around Babies and Small Children?

Any parent knows it is crucial to assess everything in the near vicinity of infants for potential risks.

Generally, it is best to keep babies and small children away from operating devices because of the risk of trapped fingers, trips, and other routine accidents arising from a child’s curiosity and lack of coordination.

Humidifiers and Dehumidifiers

Controlling moisture levels using humidifiers and dehumidifiers in a room where a baby plays or sleeps is beneficial.

Human health needs humidity to remain in the healthy range – not too dry, not too wet.

Using a whole-house humidifier or a cool-mist type eliminates the risk of steam burns if a curious toddler approaches the device. The best safety feature for use with infants is a cut-off switch when you achieve the desired humidity level.

Air Purifiers

Clean air is better than dirty air – especially for a baby, as air pollution causes numerous developmental problems.

Most air purification units will clean a room in a couple of hours, leaving you confident that our baby has a healthier sleeping environment.


Lavender or chamomile drops added to a baby’s bathwater is a piece of folk wisdom that works to calm a restless baby and promote calm sleep.

Using a diffuser to fragrance your home with gentle, baby-friendly aromatherapy oils produces the same result, but follow these aromatherapy safety tips:

  • Use the diffuser for a minimum amount of time and not while the baby is in the room.
  • Stick with baby-friendly oils.
  • Stop using the diffuser if there is any sign of respiratory distress.
  • Talk to your doctor if you have any concerns.


In the absence of clear scientific evidence for benefits or harms, it is sensible to avoid using an ionizer around your baby and small children.

If you would like them to benefit from negative ions, invest in an indoor water fountain.

Are These Devices Safe in Pregnancy?

Pregnancy is a minefield for a woman to navigate – so many Dos and Don’ts that it is hard to know what to do for the best.

Controlling moisture levels and breathing clean air will benefit your health and that of your little passenger.

Excessive dry, damp, or polluted air is known to harm you, and you want to avoid it if possible.

Breathing in aromatherapy oils and risking the use of an ionizer are optional activities that will not harm you if you avoid them.

As the best approach to a healthy pregnancy is to avoid potential harm, you can’t go wrong if you don’t use a diffuser or ionizer at this time.

If you want to use aromatherapy oils during pregnancy, consult a licensed professional and use them under supervision.

Last Word: Should You Buy One or More of These Devices?

Although humidifiers, dehumidifiers, and air purifiers are not medical devices, there is plenty of evidence that controlling humidity and pollution in your home will benefit your health and your home.

These devices make breathing easier, remove harmful particles, and although they won’t cure asthma or allergy flare-ups, they will alleviate the symptoms.

Diffusers and ionizers are more of a personal preference.

Some people find them a positive boost to their mood and well-being, and others see no benefit.

These devices tend to be inexpensive so that if you feel they might help improve your life, you can try them out without investing too much of your household budget.

You are what you eat, but the air you breathe is crucial to your health – every breath you take should energize and invigorate you, not promote a coughing fit or a struggle for your next breath.

Humidifiers, dehumidifiers, and air purifiers can help make breathing easier for everyone.


Ideal Indoor Relative Humidity Recommended by EPA.

40% Relative Humidity Deactivates Some Viruses.

The Link Between Air Pollution and Early Death.

The CDC regulates the use of ozone to protect health workers.

The FDA considers some essential oils safe for use.