Patch testing is widely used in evaluating suspected contact dermatitis. One major component of a quality patch test result is a dependable, predictable allergen supply. The allergen needs to be present at a sufficient concentration to elicit a reaction in an allergic patient. To better understand the stability of patch-test allergens, we completed a systematic review of the literature. We found that there is variability in stability among patch-test allergens and that although a few have been shown to be stable, many degrade when in storage. In most cases, expiration dates should be honored. In addition, allergen panels should be prepared as close to the time of patch test application as is possible.