Supplementing eunuchs with testosterone during their second decade, for example, causes slow progression of androgenic alopecia over many years, while testosterone late in life causes rapid hair loss within a month.An example of premature age effect is Werners syndrome, a condition of accelerated aging from low-fidelity copying of mRNA. Affected children display premature androgenic alopecia.Permanent hair-loss is a result of reduction of the number of living hair matrixes. Long-term of insufficiency of nutrition is an important cause for the death of hair matrixes. Misrepair-accumulation aging theory    suggests that dermal fibrosis is associated with the progressive hair-loss and hair-whitening in old people. With age, the dermal layer of the skin has progressive deposition of collagen fibers, and this is a result of accumulation of Misrepairs of derma. Fibrosis makes the derma stiff and makes the tissue have increased resistance to the walls of blood vessels. The tissue resistance to arteries will lead to the reduction of blood supply to the local tissue including the papillas. Dermal fibrosis is progressive; thus the insufficiency of nutrition to papillas is permanent. Senile hair-loss and hair-whitening are partially a consequence of the fibrosis of the skin. Diagnosis
The diagnosis of androgenic alopecia can be usually established based on clinical presentation in men. In women, the diagnosis usually requires more complex diagnostic evaluation. Further evaluation of the differential requires exclusion of other causes of hair loss, and assessing for the typical progressive hair loss pattern of androgenic alopecia. Trichoscopy can be used for further evaluation.
This type of tolerance is most evident with oral ingestion, because other routes of drug administration bypass first-pass metabolism. Enzyme induction is partly responsible for the phenomenon of tolerance, in which repeated use of a drug leads to a reduction of the drugs effect. However, it is only one of several mechanisms leading to tolerance. Behavioral tolerance
Behavioral tolerance occurs with the use of certain psychoactive drugs, where tolerance to a behavioral effect of a drug, such as increased motor activity by methamphetamine, occurs with repeated use. It may occur through drug-independent learning or as a form of pharmacodynamic tolerance in the brain; the former mechanism of behavioral tolerance occurs when one learns how to actively overcome drug-induced impairment through practice. Behavioral tolerance is often context-dependent, meaning tolerance depends on the environment in which the drug is administered, and not on the drug itself. Behavioral sensitization describes the opposite phenomenon. See also


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