Why does hair shed after rapid weight loss?

Noticeably increased shedding after a period of rapid weight loss, illness, surgery or major stress is a recognised pattern. The characteristic feature is the delay: it typically appears some months after the event rather than during it, which is why people often fail to connect the two.

What is happening is that a larger than usual proportion of hairs shift into a resting phase at the same time and are then shed together. It is diffuse thinning across the scalp rather than a receding pattern, and in many cases it is temporary once the underlying stress has passed.

It is worth having looked at rather than assumed. Thyroid problems, iron deficiency and other nutritional gaps can produce similar shedding and are treatable once identified, and a clinician can distinguish this pattern from other causes of hair loss.