What are chemical sensitivities?

Chemical sensitivities means when a person experiences reactions (such as brain fog, headache, rash, shortness of breath, difficulty breathing, agitation, anxiety to name only a few) when they are exposed to certain chemicals or substances. They are physically sensitive to these chemicals.

Being sensitive to chemicals comes under the heading of environmental illness. In this type of environmental illness, something in the environment is toxic, an irritant, or incitant and can cause individuals to have mild to severe and life-threatening reactions from their exposure to the chemical or substance—even when the exposure is to the tiniest amount that another person might not even notice.

What is MCS?

Multiple Chemical Sensitivity (MCS) is a term used to name the experience of being sensitive to multiple chemical substances and having mild to severe and/or life-threatening reactions when exposed to those substances. It is not a medical diagnosis (see here).

Individuals who have sensitivities to multiple chemicals are suffering from an environmental illness, typically a mast cell activation related disorder.

Current research has shown that the reactions to triggers a person experiences, (and sensitivity to chemicals is just one area of potential triggers,) have their basis in mast cell function and in mast cell degranulation. Click/Tap here to learn more about mast cells.

Mast cell disorders are medical diagnoses. A person with a diagnosed mast cell disorder—Mast Cell Activation Syndrome, for example—can also say they have MCS. However, MCS, is not the medical diagnosis and refers to symptoms. Mast Cell Activation Syndrome, in this example, would be the medical diagnosis and its symptoms include being sensitive to multiple chemicals.

I don’t understand about triggers.

The word ‘trigger’ refers to whatever chemical or substance it is that makes a person with chemical sensitivities have a reaction. The specific triggers that cause a reaction, as well as the reactions themselves, can be different for different people.

Are chemical sensitivities a mental illness?

Being sensitive to multiple chemicals and experiencing reactions to exposures to chemicals is not a mental illness. Environmental illnesses are real, physical illnesses not psychological.

The impact and effects of chemical sensitivities on a person and on their life can be devastating. People do not always know or even realize that what they are experiencing has a name. Most physicians are not trained to recognize, diagnose, or treat these disorders. Many healthcare professionals deny they exist.

What can someone do to not become worse?

People with sensitivities to multiple chemicals must avoid and minimize their exposures to the chemicals and environments that cause them to have what can often be severe and potentially life-threatening reactions. Individuals with chemical sensitivities may need to avoid small and large groups of people, public places (like libraries, buses, trains, offices, parks, restaurants,) car exhaust, certain foods, cell phones, soaps and detergents, electrical currents, plastics—and this is not a complete list of all the triggers. Environmental illnesses, especially those that may include sensitivity to various chemicals and substances, can be permanently disabling for some while others are able to continue working once reasonable accommodations are in place.

What about scented products?

A person who has chemical sensitivities has reactions to multiple chemicals. If a product is scented, it isn’t the scent to which a person reacts. The person is reacting to the chemicals (and many times to the “natural” and/or to the “organic”  substances, as well) that the product contains which combine to create a scent. They are not reacting to the smell.

An example of this is laundry detergent. It can be easy to think, after being exposed to the strong scent of a certain laundry detergent and having a reaction, that it was the “scent” causing the reaction when really it was the chemicals and substances that make up the laundry detergent and the chemicals and substances that make up the scent that triggered the reaction.

This is why people are sometimes puzzled when they still have a reaction but have switched laundry products to one without fragrance—why are they still reacting? It’s because it isn’t the “scent” that causes the reactions. It’s the chemicals and substances that make the product and the chemicals and substances that create the scent that are the triggers. It is to these chemicals and substances that people have reactions.

What do I do?

If you feel that you may have an environmental illness (such as Long COVID or other illness whose symptoms include chemical sensitivities) contact a physician to receive medical help. The information presented here is not medical advice and is in no way a substitute for receiving medical advice and treatment from a doctor.


Learn More:

About Chemical Sensitivities

About Mast Cells

About Environmental Illnesses


Expanding Horizons


Toxins in our Lives

Pesticide Information






Education & Training


The Counseling Center at CELA is not endorsing any of the above links or their content and is providing these links as informational resources only.