The mechanism of action varies from toxin to toxin, but is usually due to the production of a photoproduct. Toxins which are associated with PCD include the psoralens. Psoralens are in fact used therapeutically for the treatment of psoriasis, eczema, and vitiligo. Photocontact dermatitis is another condition in which the distinction between forms of contact dermatitis is not clear-cut. Immunological mechanisms can also play a part, causing a response similar to ACD. Diagnosis
Since contact dermatitis relies on an irritant or an allergen to initiate the reaction, it is important for the patient to identify the responsible agent and avoid it. This can be accomplished by having patch tests, one of various methods commonly known as allergy testing. The patch tests were based on the concept of a type IV hypersensitivity reaction where there is exposure of allergens to skin and checking for the development of contact dermatitis in that area. This test involves the application of suspected irritant to a part of the skin and cover it with impermeable material and attached to the skin with the help of adhesive plaster. The top three allergens found in patch tests from 2005 to 2006 were:  nickel sulfate (19.0%), Myroxylon pereirae (Balsam of Peru, 11.9%), and fragrance mix I (11.5%).The patient must know where the irritant or allergen is found to be able to avoid it.
Individuals over 40 who played over two hours doubled their chance of injury. Those under 40 increased it 3.5 fold compared to those who played less than two hours per day. History
German physician F. Runge is usually credited for the first description of the condition, calling it "writers cramp" (Schreibekrampf) in 1873. Later, it was called "washer womens elbow". British surgeon Henry Morris published an article in The Lancet describing "lawn tennis arm" in 1883. The popular term "tennis elbow" first appeared the same year in a paper by H. P. Major, described as "lawn-tennis elbow". See also
Olecranon bursitis
Radial tunnel syndrome
Repetitive strain injury

References
External links
Wilson JJ, Best TM (September 2005). "Common overuse tendon problems: A review and recommendations for treatment". American Family Physician. 72 (5): 811–818. PMID 16156339. Archived from the original on 2007-09-29. Retrieved 2006-03-11.