There are two main types of contact dermatitis, the irritant contact dermatitis and the allergic contact dermatitis. These constitute the major occupational allergic skin diseases.
Contact Irritant Dermatitis
Contact irritant dermatitis is caused by chemical, physical or biological (plants, animals) irritants. The acute form of the irritant contact dermatitis occurs following a single exposure to the offending agent, which is toxic to the skin. Severe reactions may cause the skin to slough off, producing deep necrotic ulcers. Common examples of irritants which cause contact irritant dermatitis are croton oil, phenols, kerosene, organic solvents, sodium and potassium hydroxide, lime acids etc.
The severity of the irritant reaction in CID (contact irritant dermatitis) is dependent upon the concentration of the chemical irritant. Certain levels of the concentrate produces CID, lower strengths does not. This is in contrast to the ACD (Allergic contact dermatitis), where the allergic reaction is independent of the concentration of the allergen, meaning even a small quantity is sufficient to trigger the allergic response.
Treatment of CID involves identification and avoidance of the irritants, copious washing if contact does occur, barrier creams and treatment of the dermatitis according to the stage of the eczema, the acute, sub acute and chronic eczemas.
Allergic Contact Dermatitis
Allergic Contact Dermatitis is an immunological reaction caused by the interaction of an antigen with the antibodies produced against the antigen. For ACD (allergic contact dermatitis) to occur a previous exposure and sensitization to the antigen (allergy producing substance) is required. This sensitization requires 7-21 days to occur.
If the individual is again exposed to the same allergen, within a period of 12-24 hours, an antigen-antibody reaction occurs in the skin, which causes the inflammatory changes seen in allergic contact dermatitis. This type of allergic reaction is known as the cell mediated or delayed hypersensitivity reaction.
The exact cause of the ACD can be pinpointed through patch testing with suspected allergens.
Treatment of allergic contact dermatitis involves avoidance of the allergen as far as possible and immediate treatment with topical and systemic steroids at the earliest sign of allergic contact dermatitis. Acute explosive ACD eruption can cause high levels of swelling and weeping skin lesions, especially on the face (following allergic contact dermatitis to hair dyes, for example).
How to Differentiate Between the Contact Irritant Dermatitis and Allergic Contact Dermatitis?
Differentiating between the two types of contact dermatitis is important from the preventive and management point of view.
- Contact irritant dermatitis is dose dependent: higher the amount of irritant, stronger the reaction. Allergic contact dermatitis is not dose dependent; once the individual is sensitized, even minute quantities can produce allergic reaction on the skin.
- As contact irritant dermatitis is a toxic reaction, it involves only the area of contact with the irritant. The margins are sharply defined; the reaction does not extend beyond. In allergic contact dermatitis, the reaction can occur outside area of contact, even in remote areas of the body which never came in contact with the allergen. Thus generalized allergic reaction is possibly in ACD.
- Anyone can get contact irritant dermatitis, but only sensitized individuals get allergic contact dermatitis.
Contact dermatitis, both irritant and allergic, is the major cause for occupational skin disease in many industrial and agricultural workers and needs to be addressed early in the disease process for proper diagnosis, management and control of the disease activity.
Reference
- Contact Dermatitis, in Rook’s Textbook of Dermatology, 7th Edition, 2004
- Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, Fifth Ed, 2005
Disclaimer
The information given in this article is for educational purpose only so that patients are aware of the options available. No diagnosis should be made or treatment undertaken without first consulting your doctor. If you do so, the author or suite101 will not be responsible for any consequences. The images provided are for illustration purpose only.
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