Sunday, November 2, 2014

Contact dermatitis to fragrance in facial cream.

Contact dermatitis to fragrance in facial cream.


Allergic contact dermatitis
The characteristics of allergic dermatitis are as follows:
• Previous exposure to the substance concerned.
• 48–96 h between contact and the development of changes in the 
skin.
 Contact allergy to stoma dressing.
• Activation of previously sensitised sites by contact with an allergen 
at a distant skin site.
• Persistence of the allergy for many years.

Immune mechanisms
Allergic dermatitis results from a type IV delayed hypersensitivity 
reaction in the skin. Specific antigens (usually proteins) penetrate 
the epidermis, combine with a proteinmediator and are then picked 
up by Langerhans cells. This causes T-lymphocytes in regional lymph nodes to become sensitised to the antigen. On subsequent exposure to the antigen, an allergic reaction occurs because of the accumulation of sensitised T-lymphocytes at the site of the antigen
with a resultant inflammatory response. This takes 48 h and is amplified by interleukins that provide a positive feedback stimulus to the production of further sensitised T-lymphocytes.

Irritant contact dermatitis This may be chemical or physical, has a less defined clinical course
and is caused by a wide variety of substances with no predictable time interval between contact and the appearance of the rash. Physical irritants include air conditioning, prosthetic limbs, personnel protective clothing and repetitive mechanical trauma. Chemical irritants include detergents, solvents and acids. Dermatitis occurs soon after exposure and the severity varies with the quantity concentration and length of exposure to the substance concerned.
Previous contact is not required, unlike allergic dermatitis where previous sensitisation is necessary.


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