How a follicle shapes a growing strand
A hair shaft is made by living cells deep inside a skin pocket called a follicle. As those cells multiply, harden, and move upward, they form the strand we see. The follicle’s shape helps determine how evenly that strand grows around its center. A more rounded follicle tends to produce a more symmetrical shaft; an oval or flatter one can produce a strand with unequal curvature.
That difference matters because a hair bends more readily in one direction when its structure is uneven. The bend is therefore established as the strand forms, rather than being created from scratch by rain or humidity. Moisture can still change how hair behaves temporarily, but it does not determine the basic pattern built during growth.
Why a cross section reveals the pattern
Cut straight across a strand and its outline offers a snapshot of that structure. A nearly circular outline is consistent with a shaft that grows relatively evenly around its center, so it tends to lie straight. A more elongated or flattened outline is associated with greater bending and curling.
The follicle’s geometry is part of the explanation, not a perfect predictor of every strand. Hair texture reflects how the growing follicle produces the shaft, and individual hairs can vary across a head. Still, the cross section makes the underlying idea visible: the strand’s shape begins below the skin, before the hair is long enough to curl.
