Hair Loss

脱发 · 先分清是哪一种

Place · Level 3 · Conditions

头发有生长周期 · 雄激素性脱发是 DHT 让毛囊一代代变细 (缓慢、有遗传底色) · 休止期脱发是周期被压力/疾病同步打断 (突然、通常可逆) · 分清了才知道什么真有用

Connected to · 5

regulates · 5

PCOS
The androgen excess of PCOS thins scalp follicles while coarsening facial and body hair — one hormone, two opposite-looking outcomes. Hair loss alongside irregular cycles, acne or hirsutism is a reason to check hormones.
Hashimoto's
Thyroid hormone sets the pace of follicle turnover. In hypothyroidism hair thins and the growth phase shortens, usually alongside fatigue and cold intolerance. This is the testable, reversible category — rule it out first.
Iron
Hair follicles are among the fastest-proliferating tissues in the body, so they are demoted first when iron runs low. The telogen effluvium of low ferritin regrows once iron is restored — check ferritin before buying shampoo.
Chronic Stress · HPA Axis
A marked stressor pushes a batch of follicles into telogen together, and the shedding only appears 2-3 months later. So 'I've been shedding a lot lately' usually points at something months back — an illness, a surgery, a high-pressure stretch.
Biotin
Biotin is a carboxylase cofactor and true deficiency does cause hair loss. In people who are not deficient, the extra mostly goes on to interfere with thyroid lab assays, not to grow hair — a marketing favourite.

The hair cycle

Stop 1/5

毛囊的生长周期

To understand hair loss, first understand that hair is always 'rotating shifts'.

Each hair runs a cycle: a growth phase (anagen, about 3 years on the scalp, hair growing), a transitional phase (catagen, about two weeks), and a resting phase (telogen, about 3 months, the hair paused), before shedding and being replaced by new hair. A healthy scalp has roughly 85% of follicles in anagen and about 15% in telogen (the Telogen Effluvium review).

This gives a key intuition: losing 50-100 hairs a day is normal turnover, not disease. What to distinguish isn't 'am I shedding a lot' but two things — is it 'shedding abnormally much (a problem at the shedding end)', or 'growing less and finer over time (a problem at the growth end)'. These correspond to completely different mechanisms, and completely different management.

The next two scenes cover the two commonest kinds: one where the growth end is weakened generation by generation by a hormone (androgenetic alopecia), and one where the shedding end is synchronized and disrupted by a single shock (telogen effluvium).

Read story

Educational content, not medical advice — consult a clinician.

Back

Hair Loss

脱发 · 先分清是哪一种

Place · Level 3 · Conditions

头发有生长周期 · 雄激素性脱发是 DHT 让毛囊一代代变细 (缓慢、有遗传底色) · 休止期脱发是周期被压力/疾病同步打断 (突然、通常可逆) · 分清了才知道什么真有用

Connected to · 5

regulates · 5

PCOS
The androgen excess of PCOS thins scalp follicles while coarsening facial and body hair — one hormone, two opposite-looking outcomes. Hair loss alongside irregular cycles, acne or hirsutism is a reason to check hormones.
Hashimoto's
Thyroid hormone sets the pace of follicle turnover. In hypothyroidism hair thins and the growth phase shortens, usually alongside fatigue and cold intolerance. This is the testable, reversible category — rule it out first.
Iron
Hair follicles are among the fastest-proliferating tissues in the body, so they are demoted first when iron runs low. The telogen effluvium of low ferritin regrows once iron is restored — check ferritin before buying shampoo.
Chronic Stress · HPA Axis
A marked stressor pushes a batch of follicles into telogen together, and the shedding only appears 2-3 months later. So 'I've been shedding a lot lately' usually points at something months back — an illness, a surgery, a high-pressure stretch.
Biotin
Biotin is a carboxylase cofactor and true deficiency does cause hair loss. In people who are not deficient, the extra mostly goes on to interfere with thyroid lab assays, not to grow hair — a marketing favourite.

The hair cycle

Stop 1/5

毛囊的生长周期

To understand hair loss, first understand that hair is always 'rotating shifts'.

Each hair runs a cycle: a growth phase (anagen, about 3 years on the scalp, hair growing), a transitional phase (catagen, about two weeks), and a resting phase (telogen, about 3 months, the hair paused), before shedding and being replaced by new hair. A healthy scalp has roughly 85% of follicles in anagen and about 15% in telogen (the Telogen Effluvium review).

This gives a key intuition: losing 50-100 hairs a day is normal turnover, not disease. What to distinguish isn't 'am I shedding a lot' but two things — is it 'shedding abnormally much (a problem at the shedding end)', or 'growing less and finer over time (a problem at the growth end)'. These correspond to completely different mechanisms, and completely different management.

The next two scenes cover the two commonest kinds: one where the growth end is weakened generation by generation by a hormone (androgenetic alopecia), and one where the shedding end is synchronized and disrupted by a single shock (telogen effluvium).

Read story

Educational content, not medical advice — consult a clinician.