Irritant Contact Dermatitis or ICD is a localized skin inflammation caused exogenously; that is, it is the result of direct contact of the skin with external irritants. The immune system plays no part in the development of ICD. The skin irritation is the result of a local skin response to the irritant.

The irritants, which cause irritant contact dermatitis, include a wide variety of organic and inorganic chemicals and substances, metals, environmental factors and physical factors. Acids and alkalis are the most common irritants.

Classes of irritants

Acids: Various types of acids act as corrosive irritants on the skin and produce, more or less, the same clinical features, such as, erythema, vesication and tissue necrosis. Hydrofluoric and sulfuric acids cause the severest reactions, even at low concentrations.

Hydrofluoric acid is used in the semi-conductor, glass, metal, and stone industry and is the only substance which dissolves silicon. It is also used in households to remove rust and metal stains. A hydrofluoric acid skin reaction can be very painful, since it can penetrate deep into the skin and cause tissue and even bone damage. At low concentrations, the onset may be delayed for a day, but the effect can be just as painful, as it slowly penetrates the skin.

Sulfuric acid is widely used in numerous industries, such as, fertilizers, textile, pigment, explosives and paper, to name a few. Most at risk are jewelers, electroplaters, metal cleaners and storage battery makers. Chromic acid, used in chrome plating and copper stripping can perforate the nasal septum, and nitric acid, used as rocket fuel and in laboratories, can be very corrosive.

Organic acids are, generally, less irritating than inorganic acids. Acetic, acrylic, formic and salicylic are the common irritants, when there is prolonged exposure to them. Formic acid, used in leather and natural latex manufacture, has the highest corrosive power of the organic acids.

Alkalis: Alkalis often cause more damage than acids, excepting hydrofluoric acids. Clinical features in alkali exposure generally do not show vesicles, but rather a necrotic skin, which is initially dark brown, then black and finally hard, dry and cracked. Alkalis disturb the skin barrier, denature proteins and act on fatty acids to produce soaps, which facilitate more alkali penetration deep into the skin. Some strong alkalis are sodium and potassium hydroxides and carbonate, used in bleaching, dyeing, soaps and detergents.

Cement mixed with water releases the highly alkaline calcium hydroxide, which can cause severe ulceration. The reactions appear 10 to 12 hours after exposure. Chronic irritant contact dermatitis due to repeated exposure to cement may develop over months. In cement workers, hands and lower limbs are usually affected.

Metal salts: Many salts produce clinical features, ranging from ulceration to folliculitis and pigmentary changes. Arsenic salts produce persistent folliculitis and sometimes a systemic toxicity. Widespread preventive measures are needed against arsenic, which is used in pesticide production, semiconductor and smelting industries. Cobalt salts can cause both irritant and allergic contact dermatitis. Mercuric salts, once popular disinfectants, are mostly no longer used due to risks of sensitization and their general toxicity. However, mercuric salts can be found in waste from the gold industry where the metal is used to extract gold from crushed rock.

Solvents: Many types of solvents are used in chemical reactions, metal refining and dry cleaning and nearly all cause skin irritation of varying degrees, with turpentine also causing allergic sensitization. Solvents act by impairing the skin barrier, thus increasing absorption by the skin of chemicals. Prolonged exposure can cause severe burns, systemic symptoms and sometimes even death. Repeated exposure causes erythema, scaling, dryness and eventually eczema. Coal tar solvents can cause drying and defatting from vapors alone. Ethers, esters and ketones are all irritants to different degrees.

Alcohols: Alcohols, used widely as solvents, preservatives and disinfectants in the cosmetic industry, are mild irritants, but prolonged exposure may cause irritation and toxicity. The intensity of such reactions depends on the number of carbon atoms of the alcohol. Alcohol, it is theorized, acts by disrupting the skin barrier.

Detergents and cleansers: Skin cleansers rarely cause irritant contact dermatitis, except when the skin is damaged. Detergents are a common irritant present in cleansers, cosmetics and household cleaning products. They work by impairing the skin barrier. Anionic detergents, such as, alkyl sulfates and alkyl carboxylate salts are more irritating than the ionic and amphoteric ones.

Disinfectants: Disinfectants are weak irritants and cause chronic irritant contact dermatitis due to cumulative doses. Disinfectants can be alcohols, aldehydes, phenol compounds, halogenated compounds and dyes, among others. Ethylene oxide, used for sterilization, can be a cause of burns among hospital staff. Aldehydes are more irritating than alcohols. Formaldehyde is a common sensitizer even at low concentrations because of its high chemical reactivity with proteins. Chlorine compounds, used as disinfectant, can cause skin irritation, particularly at higher temperatures.

Food: Ingredients in some foods result in some people working in agriculture, catering and food processing industries, to suffer from chronic irritant contact dermatitis. Such a condition is accepted as normal and medical advice is rarely sought. See elsewhere on this web site for common food allergens which can also work as irritants with repeated skin contact.