THE SCIENCE OF
Human
hai r grows in dif ferent
lengths, colours and textures. Aside from our
heads , common a reas of ha i r g rowth a re
apparent on arms and legs, face and pubic areas
after we hit puberty. While hair on our heads
grows continuously, requiring regular grooming,
our body hair seems to stop getting longer after
reaching a certain length, suggesting that these
hairs are of dissimilar types. What exactly are the
differences exhibited in these types of hair and
what governs their growth and appearance?
There are general ly three types of hai r s,
namely vellus hair, terminal hair and scalp hair.
Vellus hair is short, delicate, not incredibly visible
and produced all over the body. It is most easily
obser ved on children and female adults. In
comparison, terminal hair is thicker, longer and
darker in colour, more visible on males than
on females. Finally, scalp hair refers to the self-
explanatory hairs on our heads.
To begin understanding the different types of
hair, it is noteworthy to understand the general
growth stages of hair. Our heads, alone, carry
over 100,000 hairs and each independent strand
undergoes stages of growth at a different rate.
The birth of a hair begins in a hair follicle, tucked
snugly beneath the skin. Three distinct growth
phases can be observed throughout the life cycle
of a hair:
1 Anagen (growth stage)
At the anagen phase, hair grows at about
just over a centimetre per month. The length of
this phase corresponds with the length of the
hair, and is predetermined by genetics, but also
depends on hormones and other environmental
factors.
2 Catagen (intermediate stage)
The catagen phase occurs at the conclusion
of t he anagen pha s e. I t i s a s ho r t - l i ved
intermediate stage where the blood supply and
cells required in growing and producing hair is
closed off.
3 Telogen (resting stage)
Hair at this stage becomes stale and gradually
falls out. During this phase, the
hair follicle is
inactivated for about 3 months, where no growth
occurs, before the cycle begins at the anagen
phase once again. Poor nutrition or illnesses can
force hair follicles to enter the telogen phase
prematurely, where problems such as hair loss
occur.
By Hoi Yue Chan
陳凱瑜
(Diocesan Girls’ School,
拔萃女書院
)
毛髮的秘密
This article was edited to fit the needs of the Science Focus publication.
本文以「科言」所需而被更改。
W
inning article of the
Science Focus
Article Submission Competition.
「科言」
徵文比賽得獎文章。
