Hair growth rate

If scientific notation is confusing to you, learn to use it.1 We can put this hair growth rate in more convenient units ... 

Generally, the samples tested were head hair obtained from expertises or from subjects deceased from fatal heroin or cocaine overdose. Collection procedures have not been standardized, but hair is often collected from the area at the back of the head (vertex posterior), cut as close as possible to the scalp and stored in dry tubes. In this area, there is less variability in hair growth rate, the number of hairs in the growing phase is more constant, and the hair is less subject to age and sex-related influences. Occasionally, axiUaty or pubic hair have also been tested for cannabinoids. 

In eight patients to whom HL had been administered at fixed doses (2-10 mg/d) for more than 1 month, and in whom either therapy had just been discontinued or doses halved, a cross-sectional analysis of hair collected at the time of dose changing and at fixed times (1-3 months) thereafter revealed variations of hair concentrations that were time related (assuming a hair growth rate of 1.0-1.5 cm/month) to the changes in drug intake. 

Using an HPLC procedure with coulometiic detection, chlorpromazine was assayed in hair samples of 23 subjects who had been taking the drug in fixed daily doses. Chlorpromazine concentrations ranged from 1.6 to 27.5 ng/mg and was significantly correlated with the daily dose (r = 0.788, p < lO" ). With the assumption of a hair growth rate of 1 cm per month, the individual history of chlopromazine doses in all patients could be deduced from the distribution of chlorpromazine along the hair shaft. The authors concluded that these results indicate that hair could serve as an indicator of individual exposure to neuroleptics and could yield retrospective information. 

Hair. Scalp hair is another primary indicator used to assess methylmercury exposure, because the methylmercury is incorporated into the hair at the hair follicle in proportion to its content in the blood (EPA 1996d). The typical hair-to-blood ratio in humans has been estimated to be about 250 1 expressed as g Hg/g hair to mg Hg/L blood, but some difficulties in measurements, inter-individual variation in body burden, differences in hair growth rates, and variations in fresh and saltwater fish intake have led to varying estimates (Birke et al. 1972 Skerfving 1974). Once incorporated into the hair strand, the methylmercury is stable and gives a longitudinal history of blood methylmercury levels (WHO 1990). 

Zinc in Hair. Low hair zinc has been associated with poor growth in children, and has been used as a criterion for initiating supplementation studies, However, variables such as hair growth rate and external contamination from hair dyes and cosmetics can cause inconsistent results. Results from individual patients are difficult to interpret. 

Hislop et al. (1983) related the time course of MeHg elimination from blood and hair cut at the scalp with the assumption that the hair Hg concentration is proportional to the blood Hg concentration. The blood was sampled at regular intervals. The hair was sampled once and divided into 8-mm segments. The measurement of the hair-growth rate was 8 mm of growth per 20 days. The presence of a distinct maximal... 

The use of hair as a material in which to measure nicotine and cotinine has been proposed as a way to assess long-term exposure to nicotine from tobacco products. Nicotine and cotinine are incorporated into hair as it grows over time. The average rate of hair growth is 1 cm per month. Thus, measurements of levels of nicotine may provide a way of assessing exposure of a person to nicotine over several months (Al-Delaimy et al. 2002 Florescu et al. 2007). 

The concentration of fluoride in nails and hair appears to be proportional to intake over longer periods of time, taking into account their growth rate [100-103]. Exposure to fluoride may occur in the local environment at the place of residence or via occupational exposure. Daily intake from food, water, dentifrices or fluoride supplements also contributes. The major advantage of nails and hair over fluids and tissues as biomarkers for fluoride exposure is that they can easily be obtained in a non-invasive manner. In contrast to plasma, saliva and urine, whose fluoride concentrations provide a snapshot at a certain point of time and are subject to change due to recent fluoride intake and certain physiological variables, the concentration of fluoride in nails and hair is cumulative and reflects the average level of intake over a time period, but depends on how often the nails are clipped or hair cut. 

Mechanism of Action A topical antiprotozoal that inhibits ornithine decarboxylase cell division and synthetic function in the skin. Therapeutic Effect Reduces rate of hair growth. 

Eflornithine (Vaniqa) is an irreversible inhibitor of ornithine decarboxylase, which catalyzes the rate-limiting step in the biosynthesis of polyamines. Polyamines are required for cell division and differentiation, and inhibition of ornithine decarboxylase affects the rate of hair growth. Topical eflornithine has been shown to be effective in reducing facial hair growth in approximately 30% of women when applied twice daily for 6 months of therapy. Hair growth was observed to return to pretreatment levels 8 weeks after discontinuation. Local adverse effects include stinging, burning, and folliculitis. 

Although vasodilators are effective in lowering blood pressure, these drugs are associated with a number of adverse effects. Reflex tachycardia often occurs because baroreflex responses attempt to compensate for the fall in vascular resistance that these drugs produce. This side effect is analogous to the increased heart rate occurring when alpha blockers are used to decrease peripheral vascular resistance. Other common reactions include dizziness, postural hypotension, weakness, nausea, fluid retention, and headache. Minoxidil also increases hair growth on the face, ears, forehead,... 

Direct vasodilators frequently produce baroreflex-induced tachycardia, but rarely orthostatic hypotension. They are usually prescribed with a beta blocker or a centrally acting antihypertensive to minimize the reflex increase in heart rate and cardiac output. It should be noted that another member of the directly acting class of antihypertensives is minoxidil. This potent, long-acting drug has gained considerable notoriety for its use as a topical hair-restorer. Oral use can result in hirsutism (unwanted hair growth over the face as well as other parts of the body). 

Testosterone (Figure 6.13) is a chemical that controls the rate of growth of reproductive organs, hair growth and muscles. Its presence gives the deepening of the voice in males. 

Saitoh, M., Uzaka, M., Sakamoto, M., and Kobori, T, Rate of hair growth, in Advances in Biology of Skin Hair Growth, 9, Montana and Dobson, Oxford, 1969,183. 

Before evaluating the results contamination, interindividual growth rate and cosmetic hair treatment have to be taken into account. Contamination can be detected by washing procedures and examination of the solutions. If necessary, the individual rate of hair growth can be measured after hair sampling. Aggressive hair treatment... 

Beard hairs have the slowest growth rate (approximately 0.27 mm/d) and a long growth/rest cycle duration of 14-22 months/9-12 months. Beard hairs are exposed to sweat and sebum secretions, the latter being, on the contrary to scalp hairs, excreted through a duct that opens directly onto the surface of the skin. Like scalp hair, beard hair may be subject to environmental contamination and/or cosmetic treatments. In addition, when beard hair samples are obtained by shaving, they are likely to be contaminated by pieces of epidermis. Like scalp hair, beard hair follicles are of the male sexual type. 

Axillary and pubic hairs are quite similar in terms of growth rate (approximately 0.3 mm/d) and growth/rest cycle durations (11-18 months/12-17 months). They are both exposed to sweat and sebum secretions in addition to the secretions of the apocrine glands which are present only in the axilla and pubic area and discharge directly into the hair follicle rather than onto the surface of the surrounding skin. Axillary hair is less exposed to environmental contamination, but may be subjected to cosmetic treatments. Pubic hair may be contaminated by urine. Both types of hair are composed of ambosexual follicles. 

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