Editing Drug test (section)

====Alcohol====
In contrast to other drugs consumed, alcohol is deposited directly in the hair. For this reason the investigation procedure looks for direct products of ethanol metabolism. The main part of alcohol is oxidized in the human body. This means it is released as water and carbon dioxide. One part of the alcohol reacts with fatty acids to produce esters. The sum of the concentrations of four of these fatty acid ethyl esters (FAEEs: ethyl [[myristate]], [[ethyl palmitate]], [[ethyl oleate]] and ethyl [[stearate]]) are used as indicators of the alcohol consumption. The amounts found in hair are measured in nanograms (one nanogram equals only one billionth of a gram), however with the benefit of modern technology, it is possible to detect such small amounts. In the detection of [[ethyl glucuronide]], or EtG, testing can detect amounts in picograms (one picogram equals 0.001 nanograms).

However, there is one major difference between most drugs and alcohol metabolites in the way in which they enter into the hair: on the one hand like other drugs FAEEs enter into the hair via the [[keratinocytes]], the cells responsible for hair growth. These cells form the hair in the root and then grow through the skin surface taking any substances with them. On the other hand, the [[sebaceous glands]] produce FAEEs in the scalp and these migrate together with the sebum along the hair shaft (Auwärter et al., 2001, Pragst et al., 2004). So these glands lubricate not only the part of the hair that is just growing at 0.3&nbsp;mm per day on the skin surface, but also the more mature hair growth, providing it with a protective layer of fat.

FAEEs (nanogram = one billionth of a gram) appear in hair in almost one order of magnitude lower than (the relevant order of magnitude of) EtG (picogram = one trillionth of a gram). It has been technically possible to measure FAEEs since 1993, and the first study reporting the detection of EtG in hair was done by Sachs in 1993.<ref name="Kintz">{{cite book |author=Pascal Kintz |title=Analytical and practical aspects of drug testing in hair |url=https://books.google.com/books?id=IBBq180lUEAC&pg=PA305 |date=August 30, 2006 |publisher=CRC Press |isbn=978-0-8493-6450-1 |pages=305–}}</ref>

In practice, most hair which is sent for analysis has been cosmetically treated in some way (bleached, permed etc.). It has been proven that FAEEs are not significantly affected by such treatments (Hartwig et al., 2003a). FAEE concentrations in hair from other body sites can be interpreted in a similar fashion as scalp hair (Hartwig et al., 2003b).