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This measurement is not precise because human hair varies in diameter, ranging anywhere from 17 μm to 181 μm [millionths of a metre] [8] One nominal value often chosen is 75 micrometres (0.0030 in), [5] but this – like other measures based upon such highly variable natural objects, including the barleycorn [9] – is subject to a fair degree of imprecision.
181 μm – maximum width of a strand of human hair [25] 100–400 μm – length of Demodex mites living in human hair follicles; 175–200 μm – typical thickness of a solar cell. 200 μm – typical length of Paramecium caudatum, a ciliate protist; 200 μm – nominal width of the smallest commonly available mechanical pencil lead (0.2 mm)
Scalp hair was reported to grow between 0.6 cm and 3.36 cm per month. The growth rate of scalp hair somewhat depends on age (hair tends to grow more slowly with age), sex, and ethnicity. [3] Thicker hair (>60 μm) grows generally faster (11.4 mm per month) than thinner (20–30 μm) hair (7.6 mm per month). [4]
This is why many hair stylists recommend scheduling a maintenance trim every four to 12 weeks, depending on the thickness and texture of your hair. Михаил Руденко/ iStock 10.
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Thicker hair (>60 μm) grows generally faster (11.4 mm per month) than thinner (20-30 μm) hair (7.6 mm per month). [ 16 ] [ 17 ] It was previously thought that Caucasian hair grew more quickly than Asian hair and that the growth rate of women's hair was faster than that of men. [ 15 ]
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The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; [1] SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, [2] is a unit of length in the International System of Units (SI) equalling 1 × 10 −6 metre (SI standard prefix "micro-" = 10 −6); that is, one millionth of a metre (or one thousandth of a ...