The Most Common Indoor Allergy Culprits – Allergy Center – Everyday Health

Everyday Health: What are the most common indoor allergens, and what symptoms do they cause?

Beth Corn, MD (

Assistant Professor of Medicine, Clinical Immunology, Mount Sinai School of Medicine

The most common indoor allergens include dust, cockroaches, mold, and cats and dogs. These allergens often lead to postnasal drip, runny nose, nasal congestion, headache, sneezing, itchy, watery eyes, itchy skin, fatigue, and for some people, even difficulty breathing as well as wheezing.

Anna Feldweg, MD (

Clinical instructor of Medicine, Harvard Medical School, attending physician at Brigham and Women's Hospital

People are exposed to indoor allergens all year round, with a slightly more intense exposure during the cold-weather months, when homes are closed up and we are sealed in with our allergens. Allergens that are present year-round cause slightly different symptoms than allergens that we encounter just once a year, such as pollens.

Molds and mildews are less of a problem, because they are usually concentrated out of doors. However, if a home has water damage or leaky plumbing, mold and mildew can grow indoors and be a source of allergens.

Cat allergens can be present at surprisingly high levels, even in homes that don't have cats. This is because the allergen is so light that it travels through the air and can be carried indoors on the clothes of guests who have cats.

With chronic exposure to any allergen, people tend to complain of persistent nasal stuffiness, postnasal drip, cough, and irritated eyes. People with asthma may have more symptoms or need more medicine to control their asthma.

Related: A Guide to Nasal Sprays

In contrast, allergens that are encountered only once in a while are more likely to cause violent sneezing, runny nose, itchy, watery eyes, and throat irritation. Because of this difference, people are usually more aware when they have a seasonal allergy or hay fever because the symptoms are more obvious. In contrast, people who are allergic to indoor allergens may not be aware of the problem, because the symptoms are persistent, but at a lower level but. For example, a person who is allergic to dust mites may only notice that their nose is always stuffy, they have started breathing through their mouth at night, and their eyes often feel gritty.

Indoor Allergies: Top Cleaning Targets

Everyday Health: When it comes to cleaning, are certain areas around the house more important than others for people with indoor allergies?

Beth Corn, MD ( There are two types of areas in particular that are very high in allergens. First, bedrooms, since dust mites that produce dust live in mattresses and pillows. Carpets also collect a lot of dust, and people often have these in the bedroom. Secondly, allergens tend to be at higher levels in damp areas such as bathrooms and basements, as these are firm breeding grounds for mold.

Anna Feldweg, MD ( People who don't have allergies should not think that cleaning their house a certain way is going to keep them from getting allergies. It isn't that simple, and genetic factors probably have more to do with it than anything a person can control. However, for people who already have allergies, there are some really basic things people should know about that can help a lot.

If a person has allergies to indoor things, then they should focus their cleaning and other efforts on the rooms in which they spend the most time. This is usually the bedroom and often one other room, such as the study or TV room, in which they typically relax.

Beware of Cleaning Products With Toxic Chemicals

Everyday Health: Can you give us your list of top household products containing toxic chemicals and tell us how to use them properly (if at all)?

Beth Corn, MD ( Tolerating chemicals is an individual thing, that is, every person is different in their reaction. What bothers one person can often be tolerated by another. Since many allergic people have asthma, they often do better around fragrance-free products.

Related: What Is a Fragrance Sensitivity?

Anna Feldweg, MD ( The most common toxic household product, and one that has clearly been shown to be harmful to some people even when used as directed, is chlorine bleach and the various products made with it. Aside from bleach, a variety of cleaning products contain very toxic chemicals, such as organic solvents. Foaming cleaners designed to remove spots from furniture and carpets are an example. Chemical carpet cleaners are another. If you have small children or pets, I would not use these chemicals, as children and pets roll all over the floor and put things into their mouths and could get more exposure than adults. Chemical oven cleaners are very irritating, and it is better to have a self-cleaning oven that removes grime itself when set at high temperatures.

Keeping Your Home Clean Naturally

Everyday Health: Is it possible to keep your bathroom and kitchen clean and germ-free without using harmful chemicals?

Beth Corn, MD ( That is all relative. What is harmful to one person may not be harmful to another person. Minimizing humidity in these areas is one simple way. Using a damp mop cloth to keep the floor clean is also an easy way to start.

Anna Feldweg, MD ( It is certainly possible to get a bathroom and kitchen free of visible dirt without harmful chemicals, and it is probably not necessary to attempt to get these rooms absolutely germ-free.

Bathrooms and kitchens in public buildings, restaurants, or hospital settings should be cleaned with the goal of killing and removing all bacteria, with harsh chemicals if necessary. But for routine cleaning at home, soap and water is adequate for most jobs.

One of the dirtiest areas is the kitchen sink, but periodically soaking the sink with hot water and dish detergent (as you would when washing dishes by hand) is adequate to kill most harmful bacteria. Cutting boards and utensils that have been used to cut meat can be washed with hot water and soap or put through a hot cycle in the dish washer.

Can a Home Be too Clean?

Everyday Health: When it comes to allergies, is there such a thing as keeping a home too clean?

Beth Corn, MD ( There are studies that state that the reason there are so many allergic people is because we live in an environment that's too clean. It's called the hygiene hypothesis.

That said, keeping dust and mold under control is important. Using dust mite covers over your mattress and pillows is equally important. Removing carpets and dust collecting items such as stuffed animals, books, and curtains from the bedroom can help, as well as keeping a pet out of a pet-allergic person's bedroom.

Anna Feldweg, MD ( There probably is such a thing as keeping a home too clean, but I don't think anyone knows how to define that. This question relates to the bigger question of whether bacteria and microbes help us as much as they harm us. The answer is most certainly yes, because our bodies are teeming with bacteria that should be there and keep us healthy, but the details about whether this applies to allergies are less clear.

Related: Key Questions About Allergies

One of the theories about why allergies are increasing is that humans are not getting exposed to as many bacteria and other microbes as we were for most of our evolutionary history. For many thousands of years, we drank dirty water and had no way to keep food from spoiling, and we were stricken by a variety of illnesses beginning shortly after birth. If we got an infection, we either overcame it using only our immune systems, or we died.

Now, we have eliminated much of that exposure through cleaner food and water, vaccination to prevent many childhood illnesses, and antibiotics that kill bacteria quickly when we do get infected. It is very possible that all those bacteria and microbes interacted with the human immune system in a way that made it stronger and more effective.

Allergic disease occurs when the immune system overreacts to something that it should ignore (like a protein in dust mite feces or in pollen from a plant) and many researchers think that allergies develop with the immune system that is not adjusting properly to the environment. It is possible that we have become sufficiently disconnected from the microbes around us that we are suffering for it. So there may be such a thing as a "too clean" home, but simply giving up housework is unlikely to fix the problem. Instead, we really need to understand the details of how our immune systems interact with the world first.

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