What is contact dermatitis and can this type of reaction affect dental hygienists?

Along with non-specific and Type I allergic reactions, contact dermatitis in the form of a Type IV or delayed hypersensitivity reaction can occur.  These forms are different from the Type I immune reaction in they do not involve antibodies, but rather sensitized lymphocytes. The Type IV hypersensitivity involves CD 4+ T-lymphocytes and as a result, clinical symptoms take longer to become manifest. This abnormal cellular immune response is typically localized and observed as a localized, delayed contact dermatitis. The visible reaction is delayed since lymphocytes and other inflammatory cells must migrate to the area where the inciting chemical or other allergen is located.  Thus, the reaction can take 12 to 24 hours or longer to become observable. The slow forming, well-demarcated lesion is the result of chronic inflammation into the affected area. A common example of contact dermatitis is seen with people who suffer from a poison ivy allergy. The allergenic poison ivy oil, called urishiol, is found primarily on the leaves. A person may be initially sensitized when they touch the plant’s leaves.  Following a subsequent challenge of the now allergic person, sensitized lymphocytes and other chronic inflammatory lymphoid cells migrate to where the allergenic chemical is found on surface epithelial cells, subsequently “walling” the whole area off. This reaction causes necrosis and scabbing, which lasts for about 4 days.