What Is Multiple Chemical Sensitivity (MCS)?

Multiple chemical sensitivity (MCS) is a diagnosis in which exposure to substances like pesticides, industrial fumes, detergent, and petroleum is thought to cause symptoms ranging from headache, fatigue, and muscle pain to shortness of breath, memory problems, and depression.

While MCS is considered controversial and is not recognized by the American Medical Association or the World Health Organisation, there is some evidence supporting the diagnosis.

This article takes a look at symptoms and causes of multiple chemical sensitivity, including how the condition is diagnosed and treated. It also takes an unbiased look at the controversy and the evidence supporting and challenging the diagnosis.

What Is Multiple Chemical Sensitivity (MCS)?

Mutiple chemical sensitivity was first proposed as a disease entity in the 1950s by a physician and allergist named Theron Randolph.

Randolph proposed MCS as an intolerance to certain environmental chemicals that lead to chronic, recurring illness and disability. Symptoms of MCS develop based on the types, duration, and severity of the exposure. As such, there isn't a unique profile as to how MCS "looks."

While the same can be said of many other diseases with diverse presentations—including lupus, multiple sclerosis, or psychiatric illnesses—the lack of a clear definition or disease pathway (pathogenesis) has led some to question how to approach MCS in practice or theory.

To avoid dismissing a condition thought to affect a significant portion of the population, the World Health Organisation (WHO) acknowledged the existence of "a disease of unclear pathogenesis" in 1996 and proposed a new entity called idiopathic environmental intolerance (IEI),

According to the WHO, IEI can be diagnosed based on the following criteria:

1. The disease, not present from birth, must produce multiple recurring symptoms.
2. The symptoms must be closely linked to "multiple environmental influences" that are otherwise well tolerated by the majority of the population.
3. The symptoms cannot be explained by any other causes.

Given the broadness of the definition, many practitioners question how useful the WHO criteria are in clinical practice. As a result, some experts have taken a more cause-and-effect approach, defining MCS simply as:

1. Symptoms that appear when exposed to chemicals in the environment at doses that are usually harmless.
2. Symptoms that then disappear once the chemicals are removed.
   

Symptoms of MCS

There are many possible symptoms associated with MCS. They vary significantly from person to person and tend to come on gradually in these two phases:

• Sensitization: This phase involves symptoms that develop when a person is exposed to a chemical once in a while. 
• Triggering: This phase causes symptoms to develop after exposure to many or a larger number of chemicals.

Regardless of the phase, if a person has MCS, they may experience symptoms such as:

• Nausea
• Dizziness
• Headaches
• Upper respiratory discomfort
• Runny eyes
• Pain in the throat and chest
• Fatigue
• Inability to concentrate
• Memory issues
• Changes in mood state, such as depression or anxiety
• Joint pain
• Upset stomach
• Hyperventilation
• Chest pain
• Excessive sweating
• Heart palpitations
• Weakness
• Generalized chronic pain
• Shortness of breath
• Rapid breathing
• Confusion
• Asthma
• Skin rashes

People who have MCS may not experience all of the symptoms mentioned above.

What Causes MCS?

The cause of MCS is not well understood because many in the medical community still deny it as a disease entity.

Some research suggests that it could be a psychogenic illness as many of the symptoms are similar to those seen in mood and psychological disorders, which include:

• Panic disorder
• Post-traumatic stress disorder (PTSD)
• Depression
• Anxiety
• Somatization disorders, which presents with physical symptoms driven by emotional distress

There is also little evidence to support a physical illness because of a lack of research as well as a lack of concrete findings in the available studies.

How Is MCS Diagnosed?

There are no criteria or lab tests designed to diagnose MCS. Since many healthcare providers believe that it is psychogenic, meaning driven by psychological illness, they may conduct evaluations to determine if a person has a mood disorder.

Since there are no medical tests to diagnose psychological diseases, these evaluations will primarily focus on a person’s thoughts, feelings, experiences, and behaviors in relation to their symptoms.

An older study published in 2009 found that people with MCS can be diagnosed using exposure tests, which work by exposing a person to the chemical in question to see which symptoms develop. This type of test is likely only used by healthcare providers who believe MCS to be physical in nature.

How Is MCS Treated?

The medical community is still determining what causes MCS and what is happening within the body to drive symptoms. Because of that, no effective or proven treatments are available specifically for MCS. That said, if a psychological disorder is driving the symptoms, you may be prescribed:

• Antidepressants
• Antianxiety medications
• Sleep aids

The lack of available treatments can make it hard to cope with symptoms, but many people find relief on their own by:

• Identifying their trigger chemicals and avoiding them
• Keeping a journal to track exposure to allergens that may be setting off symptoms and avoiding them in the future
• Seeking therapy or other counseling services to address mood disorder symptoms that are often present in MCS

Other Conditions Associated With MCS

MCS is often associated with other conditions, such as fibromyalgia (FMS), myalgic encephalomyelitis (ME), and chronic fatigue syndrome (CFS). Medical researchers have coined a term for these types of disorders, which is "central sensitivity syndromes."

These syndromes have many of the symptoms found in MCS, and they are often considered psychogenic as well because it can be hard to pinpoint a physical cause through laboratory tests and examinations.

Why the Debate and Controversy?

A lot of the debate surrounding the existence of MCS and the validity of the diagnosis stems from how the definition has evolved since the 1950s.

From the start, MCS was considered controversial as it was based on a definition of "allergy" that Theron Randolph insisted on but had little to do with how allergies actually develop.

Since that time, MCS has been linked to multiple disorders with equally unclear definitions and causes, including Gulf War syndrome, fibromyalgia, chronic fatigue syndrome (CFS), sick building syndrome (SBS), and electromagnetic radiation exposure (ERE).

In some cases, the definition of MCS (exposure to usually harmless chemicals) clashed with disorders in which harmful substances were involved.

This and other inconsistencies cast a shadow of doubt over a condition that is currently unrecognized by the American Medical Association, the American Academy of Allergy, the World Health Organisation, or any other major public health authority.

However, this should not suggest that MCS is entirely unsupported by research.

While much of the evidence is based on various definitions of MCS—some specific and others subjective—this shouldn't dismiss the fact that a growing number of people are recognizing and reporting illnesses to environmental chemicals that should not be causing illness.

Among the reports:

• A 2015 Japanese study in the Archives of Environmental and Occupation Health reported that 7.2% of 7,245 adults surveyed reported symptoms consistent with MCS.
• A 2017 report from the Canadian Ministry of Health reported that 0.9% of males and 3.3% of females were diagnosed with MCS by a healthcare provider.
• A 2019 study from the University of Melbourne reported that 6.5% of adults reported symptoms of MCS and that 18.9% had adverse reactions to multiple chemicals.
• A 2018 Australian study in the Journal of Occupational and Environmental Medicine reported a 200% increase in the number of self-reported cases of MCS and a 300% increase in MCS diagnoses from 2006 to 2016.
• A 2020 study from the University of Texas Health Science Center at San Antonio reported that 13% of patients surveyed met the diagnostic criteria for MCS.

Opinions are starting to evolve among some treaters who have begun to recognize MCS as a viable—if largely misunderstood—disease entity. In Spain, MCS has been recognized as a disease since 2014 and is listed as a medical condition in that country's ICD-10 (International Classification of Diseases, 10th Revision).

Talk to a Healthcare Provider

Because MCS is so controversial, many people must find their own treatments through trial and error. This process can go much smoother if you find a healthcare provider that works with you on your MCS symptoms without being dismissive of what you’re experiencing.

Before going through specialized treatments that can take time and money or possible renovations in your home to remove chemicals that may trigger symptoms, always seek help from a medical professional.

Be sure to contact more than one healthcare provider, as not all believe that MCS is a physical illness that can be treated.

Summary

MCS is a controversial disease driven by environmental exposure to certain chemicals. Many people with MCS struggle to find help for their symptoms because not everyone in the medical community sees it as a physical disease. Because of that, people are often referred to psychologists or other healthcare providers specializing in mood disorders to find something to relieve symptoms, of which there is a vast array.

The lack of research surrounding MCS has made it difficult to pinpoint a cause. However, many factors can trigger symptoms after exposure to a particular chemical. If you are experiencing the symptoms of MCS but have yet to seek help, contact a healthcare provider. They can assist you in finding out if you have MCS and what you can do about it.