Lots of information about skin patch testing for the two types of contact dermatitis (inflammation of the skin, caused by possible allergic substances): irritant contact dermatitis and allergic contact dermatitis. The site explains everything you need to know about skin patch testing.

Although written for the UK, the skin patch test is performed the same way in the US. This article gives a great overview of how skin patch tests are performed and why this particular test would be used.

Good introduction to a popular kind of test. The site is easy to read and understand and is not loaded with too much medical jargon. I liked the page even tho it does not cover more than a brief mention of nickel.