aç, homojen bir yapıya sahip gibi görünse de aslında oldukça karmaşık olan biyolojisi kısmen anlaşılmıştır.1 Memelilerde saç; protein (%65-95), su (%15-35), lipit (%1-9) ve minerallerden (<%1) oluşan deri eklerinden biridir. Saç şaftında korteksi çevreleyen bir kütikül bulunduğu gibi, bazı saç tiplerinde santral medullayı çevreleyen ilave bir kütikülde bulunmaktadır.2 Saç apokrin, sebase ve ter bezleriyle yakın ilişkide olan cildin A An na ah h t ta ar r K Ke e l li i m me e l le er r: : Saç; ilaç; birikim; kötüye kullanım A AB BS S T TR RA AC CT T In recent years hair has become a fundamental biological specimen, alternative to the usual samples blood and urine, for drug testing in the fields of forensic toxicology, clinical toxicology and clinical chemistry. Analytical results of drugs of abuse in hair provide useful information on chronic drug use. They are valuable to presume the history and severity of individual drug abuse and to provide supplementary information on drug use to facilitate interpretation of urine drug analysis. Hair testing has larger detection window. The sample collection is non-invasive. Another advantage of hair samples is that it can be stored at room temperature and do not need to be analyzed quickly after they are collected. Hair analysis is also used for detection of gestational drug exposure, doping control and detection of alcohol abuse. It has been reported that drugs are incorporated into hair by binding to such intracellular components as melanins, lipids, and proteins. It has been proposed that drugs and substances can enter into hair during at least 3 stages: from the blood during hair formation, from sweat and sebum, and from external environment. The aim of this review is to document and discuss the mechanisms of drug or substance accumulation in hair and its influencing factors, application of hair analysis.