Auckland Allergy & Eczema Clinic

Chemical Sensitivity, "Multiple Chemical Sensitivity Syndrome" & Psychoneuroimmunology

Chemical Sensitivity, 
"Multiple Chemical Sensitivity Syndrome"
& Psychoneuroimmunology

Chemical sensitivity is a loose term describing a group of clinical conditions caused by environmental chemicals.

Immunological sensitivity (hypersensitivity or allergy) 

Causes inflammation from exposure to environmental allergens, which are usually natural "chemicals", but may be manmade. These chemicals commonly cause Allergic Contact Dermatitis.

Nonimmunologic sensitivity

Nonimmunologic sensitivity to environmental chemicals causes irritation or toxicity of the skin or respiratory tract depending on route of exposure.

Multiple Chemical Sensitivity

Multiple Chemical Sensitivity has been described under various names since the 1940s. It is a syndrome in which multiple symptoms reportedly occur with low-level chemical exposure. MCS has been rejected as an established organic disease by most of the mainstream Allergy & Immunology Associations.

Allergic (Immunologic) Chemical sensitivity

All allergens are chemicals, and the typical non-occupational allergic diseases are caused by high molecular weight naturally occurring proteins. Many occupational allergens belong to a defined low or high molecular weight synthetic chemical.

Occupational Allergy

Occupational allergy is defined as allergy caused by exposure to a product that is present (only) in the workplace. The product should be specific to the workplace and causally related to the disease.

Occupational allergy can affect the lungs (asthma), the nose (rhinitis), eyes (conjunctivitis) and the skin (dermatitis).

Common Chemical Allergens causing Allergic Contact Dermatitis

  • Balsam of Peru – a wood extract from S. America. Used to be used in many cosmetics, creams, & flavourings. Decreasing use. 
  • Caine mix (Benzocaine) – are local anaesthetics that are used mainly in nonprescription topical medicaments which are designed to ease pain & pruritus. 
  • Cobalt – Found in many metal-plated objects 
  • Chromium (Potassium dichromate) – found in chrome steel or chrome-nickel-steel alloys (stainless steel) and other chrome plated metals. Also found in cement, tanned leather & textiles
  • Cinnamic aldehyde – Warm spicy odour with a taste of cinnamon. It is found in perfumes, toothpaste, cosmetics, foods (Cola, chewing gums, candy) & spices. 
  • Colophony (Rosin) – is a yellow natural residue left after distilling the volatile oils from pine tree. It is found in paper & paper products, printing ink, adhesive tapes & bandages, cosmetics, varnishes, waxes & paints.
  • Epoxy resins – found in strong, two-part adhesive
  • Ethylenediamine – emulsifier & stabilizer found in creams and nose drops 
  • Formaldehyde – the initial compound in the manufacture of several plastics and synthetic resins. Residual amounts are released from such products. Formaldehyde releasing preservatives are widely used in cosmetics, cleaning products and many industrial products.
  • Fragrances – are found in most cosmetics, personal care products, & household products (room fresheners, insect repellants, detergents). 
  • Imidazolidinyl urea – is a biocide found in cosmetics and over-the-counter topical drugs. 
  • Lanoline (wool grease) – is used in cosmetics and pharmacologic preparations because of its emollient & moisturizing properties.
  • Mercapto compounds - are vulcanization accelerators used in rubber products.
  • Methacrylates – are plastic monomers found in cosmetics (artificial nails), dental (dentures, fillings), & Medical products (adhesive tapes, contact lens, hearing aids)
  • Neomycin – used to be the most widely used topical antibiotics & became the most common sensitizer in topical antibacterial preparations. It is not as widely used these days, but is still around.
  • Nickel – found in costume (cheap) jewellery and other metal objects (coins, keys, zippers, buttons). Commonest cause of allergic contact dermatitis.
  • Parabens mix – are the most used topical preservatives. Found in several medical creams, lotions, pastes & several cosmetics
  • p-Phenylenediamine (PPD) – is a blue-black aniline dye. It is found in permanent hair dyes, many dyed textiles, leather, & fur. May also be found in dark cosmetics, black rubber, & printing ink.
  • Quaternium 15 – preservative found in cosmetics. It is a formaldehyde releaser
  • Thiuram Mix – found in almost all rubber products & adhesives for leather and vinyl products

Chemical Allergens causing Occupational Asthma (OA)

The causes of OA can be classified into high- and low-molecular weight compounds. High molecular weight compounds are often from biologic sources and induce asthma through an IgE-mediated (immune) mechanism. The majority of low-molecular-weight compounds are highly reactive and induce asthma through a non-IgE-dependent mechanism.

Low molecular weight Inorganic allergens

  • Ammonium persulfate – Beauty operator / Hairdressers
  • Metal salts – Aluminium, Chromium, Cobalt, Nickel, Platinum
    Low molecular weight Organic chemicals
  • Acrylates – Orthopedists, Nurses
  • Amines – Beauty, plastic & rubber industry
  • Acid anhydrides (also irritants) – used in the synthesis of plastcizers & for producing epoxy 
  • Azo compounds – Textile workers, Clothes dyeing
  • Isocyanates (commonest cause of OA) – Spray painters, Plastic, rubber & foam manufacture 
  • Plicatic acid
  • Polyvinyl compounds
  • Styrene compounds

Diagnosis of low molecular weight (LMW) chemical sensitivity

Some low molecular weight chemicals like acid anhydrides, platinum salts, persulfates may act as haptens (combine with endogenous, body proteins to become allergenic) and stimulate IgE antibodies. However, many LMW agents, including isocyanates and glutaraldehyde, cause occupational asthma, but induce specific IgE antibodies in only a minority of affected workers. Skin testing does not adequately assess the response to LMW antigens, it is almost useless for most LMW agents, but is a good diagnostic tool for workers sensitized to platinum & other metallic salts, and to persulfates.

High Molecular weight allergens

  • Animals – Lab workers (technicians, scientists), breeders
  • Antimicrobials – healthcare workers, pharmaceutical
  • Flour – Bakers & other food processors
  • Fungi
  • Enzymes – Detergent workers, Pharmaceutical
  • Gums
  • Insects – Grain, farm & dock workers 
  • Latex – Glove maker, healthcare workers
  • Mites
  • Pollens

Diagnosis of High Molecular weight (HMW) chemical sensitivity

Most HMW agents are complex polypeptides that act as complete antigens and stimulate IgE antibodies (e.g. animals, flour, latex, foods, mites etc)

Common causes of Occupational Asthma and related jobs

  • Isocyanates – Spray painters, plastic workers, mechanics, & electric processors.
  • Flour – Bakers & other food processors
  • Grain – Farmers or farm workers
  • Glutaraldehyde – Nurses, dark room technicians, radiographers
  • Wood Dust - Wood workers
  • Latex - Nurses, laboratory technicians
  • Solder / Colophony - Solderers, metal or electric processors
  • Laboratory animals - Laboratory technicians, scientists and assistants
  • Resins & glues – Metal & electrical processors

Multiple Chemical Sensitivity (MCS) Syndrome Or Idiopathic Environmental Intolerance (IEI)

MCS is the term used to describe people with multiple symptoms reportedly occurring with low-level chemical exposure. The term preferred by the National Institute of Environmental Health Sciences (NIEHS) is Idiopathic Environmental Intolerance (IEI), which is defined as a "chronic recurring disease caused by a person's inability to tolerate an environmental chemical or class of foreign chemicals".

Several theories have been put forward to explain the cause of MCS, including allergy, toxic effects, neurobiological sensitization, and a complex gene-environment interaction. There is insufficient scientific evidence to confirm a relationship between any of these possible causes and symptoms.

MCS has been described under various names since Theron G. Randolph first described it in the 1940s. Some of the other names include: allergic toxemia, cerebral allergy, ecologic illness, immune system dysregulation, total allergy syndrome, total environmental allergy, 20 th century disease. These labels overlap with Sick building syndrome and Gulf War Syndrome and other politically controversial diagnoses.

Symptoms associated with MCS include:

  • Depression, irritability, mood swings
  • Dizziness, lightheadedness, drowsiness & headaches
  • Fatigue & mental exhaustion
  • Sneezing, runny or stuffy nose, wheezing, skin rashes 
  • Chest pains, muscle & joint pains
  • Urinary frequency, pounding heart, upset stomach
  • Tingling of the fingers & toes

Exposures Precipitating Symptoms of MCS

  • Aerosol air freshener
  • Aerosol deodorant
  • After shave lotion, colognes, perfumes
  • Asphalt
  • Cigar & cigarette smoke
  • Diesel exhaust, diesel fuel & Gasoline exhaust
  • Dry-cleaning fluid
  • Floor cleaner & furniture polish
  • Hair spray
  • Insect repellant & insecticide spray
  • Laundry detergents
  • Nail polish & remover
  • Paints & paint thinner
  • Shampoo

Is MCS a real syndrome or a psychiatric disorder?

In an environmental health sciences meeting in Brisbane, Australia, several years ago, there was a debate on MCS, and the proponents who believed that it was simply a psychiatric disorder won the debate.

A study by Canadian researchers in 2000 (J Allergy Clin Immunol. 2000; 105(2): 358-363) suggests that patients with Idiopathic Environmental Intolerance (IEI), or MCS display high anxiety sensitivity similar to patients with panic disorder under controlled conditions.

In this blinded study patients inhaled differing concentrations of oxygen and CO2 and asked to rate each panic symptom on an objective Diagnostic Symptom Questionnaire.

The investigators concluded that "a high rate of anxiety response to inhaled CO2, among IEI patients shows a tendency to over report and catastrophically misinterpret benign physical symptoms, a consistent finding among patients with panic disorder" The authors suggested that a psychological assessment should be considered in all patients with IEI.


Psychoneuroimmunology is a research field in which scientists are trying to understand how psychological stress can affect the complex inter-relationship between the immune system, central nervous system, and endocrine system.

The term "psychoneuroimmunology" was coined by Ader & Cohen (1). In a landmark experiment, they demonstrated how the immune system undergoes classical conditioning (Pavlovian). Rats were given a pairing of a neutral stimulus (saccharin) followed by the unconditioned stimulus (cyclophosphamide), which was followed by suppression of the immune system. After repeated pairing of the neutral stimulus & the unconditioned stimulus, when rats were subsequently given saccharin alone they had an immunosuppressive response.

This finding was extended by Russell (2) to a learned histamine response in guinea pigs. In his simple experiment an immunologic challenge causing histamine release was paired with the presentation of an odour. Subsequently, the guinea pig showed histamine release when presented with the odour alone.


•  Ader R, Cohen N. behaviorally conditioned immunosuppression. Psychosom Med 1975 37: 333-40

•  Russell M, Dark KA, Cummins RW, Ellman G, Callaway E, Peeke HV, Learned histamine release. Science 1984 17; 225:733-4