The moisture in African descent hair seems to be less than Caucasian and Mongolian/Oriental hair and one reason for such deficiency of moisture could be the twisted ribbon-like structure of the African descent hair. The other reason for the deficiency of the moisture in African descent could be that sebaceous glands within the African scalp are often less active and secrete inadequate amounts of sebum—the body's own natural brand of conditioner and hairdress. Therefore, the scalp is relatively dry and so is the hair since there is less natural oil to be distributed along the hair shaft. And, too, the oil that is secreted may find it harder to travel down the hair shaft because of the strands' excessive curliness, thus further contributing to dryness.
Contrarily, Caucasians tend to have hyperactive sebaceous glands, hence the widespread practice of daily shampooing. The lower moisture contents of African descent hair may be a contributor to its relative fragility.
The Static Charge in the Hair
African descent untreated hair develops a highly negative electrostatic charge (-25.4 KV/m). Upon relaxing African-descent hair with alkali metal hydroxide creams, [i]the charge changes to + 25.9 KV/Meter. In contrast, Caucasian hair develops a very low positive electrostatic charge of +6.6 KV/M. The relatively high negative charge acquired by dry African descent hair during combing may be due to the extraordinarily high degree of pulling force required to pass the comb through the mass of entangled hair fibers . Another reason could be that a very low amount of 18 – MEA on African descent hair contributes toward higher static charge[ii]. The combing of untreated or chemically straightened African descent hair develops a significantly higher electrostatic charge than does Caucasian hair. This relatively high electrostatic charge produces a “balloon effect” and contributes to higher degree of hair unmanageability)[iii].
The Impact of Humidity
In truth, humidity impacts all hair in a similar manner. Under high humidity, African descent hair, which is styled counter to its natural texture tends to "go back home" to its original state. Curls in naturally straight hair will droop; wavy or curly hair worn in a straight style will return to its frizzy/crinkly state; excessively curly hair will start to frizz extensively.
With the latter hair type, however, the impact of humidity is simply more noticeable and the transition back to the original texture seems more dramatic. Even when African-American hair is chemically relaxed to alter the natural texture, high humidity causes the hair shaft to swell, and hair reverts back somewhat towards its original texture. This is because relaxers are meant to remove a significant amount of the excessive curliness—not all of it.
[i] AN Syed. (2006). Hair Straightening, In The Chemistry and Manufacture of Cosmetics. Ed: Mitchel Schlossman, Allured Publishing: Carol Stream, IL.vol. II, p. 539.
[ii] Breakspear, S., Smith, J.R., Luengo, G. (2005). Effect of the covalently linked fatty acid 18 – MEA on the nanotribology of hair’s outermost surface. Journal of structural Biology, 149: 235-242.
[iii] WE Morton and JWS Hearle. (1986). Physical Properties of Textile Fibres. The Textile Institute: Manchester, UK. Student Edition, p. 529.