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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.
100 μm – average diameter of a strand of human hair [25] 100 μm – thickness of a coat of paint; 100 μm – length of a dust particle; 120 μm – the geometric mean of the Planck length and the diameter of the observable universe: √ 8.8 × 10 26 m × 1.6 × 10 −35 m; 120 μm – diameter of a human ovum
Oval and other shaped fibers are generally more wavy or curly. The cuticle is the outer covering. Its complex structure slides as the hair swells and is covered with a single molecular layer of lipid that makes the hair repel water. [7] The diameter of human hair varies from 0.017 to 0.18 millimeters (0.00067 to 0.00709 in). [10]
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 ...
The original hair type chart, also known as the hair typing system, was created by Andre Walker, Oprah Winfrey's hairstylist, in the 1990s. He debuted the system on Winfrey's show to promote his ...
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Before the establishment of the decimal metric system in France during the French Revolution in the late 18th century, [4] many units of length were based on parts of the human body. [5] [6] The Nippur cubit was one of the oldest known units of length. The oldest known metal standard for length corresponds to this Sumerian unit and dates from ...
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]