How is this possible? Hair is formed in the dermis from a cluster of matrix cells that make up the follicle. During the growth phase, metabolic activity is greatly increased, exposing the hair to the internal metabolic environment. This includes the extracellular fluids, circulating blood, and lymph. As the hair reaches the surface of the skin, its outer layers harden, locking in the metabolic products accumulated during this period of hair formation. Hair is the second most metabolically active tissue and by the very nature of its formation as a biological sample, may provide a permanent record of metabolic activity occurring within the body during its period of growth. This testing is the best test for food allergy done through hair analysis. Food allergy testing by hair is becoming more popular for both adults and children. We do this test for food allergies in our Pittsburgh office.