The cause of your hair loss usually reveals itself through three clues: the pattern, the speed, and the timing. Gradual thinning at the hairline or part points to genetics; sudden diffuse shedding a couple of months after a stressful event points to stress; thinning alongside fatigue or weight changes points to hormones or the thyroid. The catch is that these causes frequently overlap, which is why a scalp exam plus targeted bloodwork is the most reliable way to know for sure. At True Roots in La Canada Flintridge, that evaluation is physician-led by board-certified Dr. Luis Valle.
Clue 1: the pattern
Where you are losing hair tells you a lot:
- Receding hairline or thinning crown (men), widening part (women): classic androgenetic alopecia, the genetic pattern.
- Diffuse thinning all over: points toward stress, thyroid, hormones, or nutritional causes rather than genetics.
- Round, patchy bald spots: suggests alopecia areata, an autoimmune cause.
- Thinning at the edges or where hair is pulled tight: suggests traction from styling.
Clue 2: the speed and timing
- Slow and gradual over years: typical of genetic pattern loss.
- Sudden, heavy shedding 2 to 3 months after a trigger: typical of telogen effluvium (stress, illness, surgery, childbirth, crash dieting). The delay is the giveaway, since the shed follows the stressor by a couple of months.
- Rapid or patchy: warrants prompt evaluation to rule out autoimmune or medical causes.
Could it be stress?
Yes. Major physical or emotional stress can push many follicles into the resting phase simultaneously, leading to noticeable shedding about two to three months later. This telogen effluvium is usually temporary and often reverses once the stressor resolves. The tricky part is that stress shedding can sit on top of genetic thinning, making things look worse than one cause alone would, which is one reason self-diagnosis is unreliable.
Could it be hormones?
Often, yes. Hormonal causes are common and very treatable, which makes them worth checking:
- Thyroid disorders (both under- and overactive) cause diffuse thinning, often with fatigue or weight changes.
- Pregnancy, postpartum, and menopause shift hormones in ways that trigger shedding or thinning. See postpartum and menopausal hair loss.
- PCOS and androgen excess can drive thinning in women.
- Low testosterone or DHT-related changes play a role in men.
Because these are identifiable on bloodwork, testing thyroid and relevant hormones is a standard part of a good evaluation.
Could it be genetics?
Genetic pattern hair loss is gradual, follows a recognizable pattern, and tends to run in the family. If your thinning matches the classic male or female pattern and has progressed slowly over years, genetics is the likely driver, though a deficiency or hormonal issue can still be layered on top. The only way to separate "purely genetic" from "genetic plus something treatable" is an evaluation.
What bloodwork reveals
Targeted labs are what turn guesswork into answers. A typical hair-loss workup checks iron and ferritin, vitamin D, B12, thyroid function, and relevant hormones. These tests routinely uncover treatable contributors, and correcting them both improves hair and helps any other treatment work better. For the full list of possibilities, see our overview of why hair thins.
When to see a doctor
See a physician if your hair loss is sudden, patchy, rapid, paired with other symptoms, or simply persistent and bothering you. Early evaluation matters for two reasons: many of the most effective treatments, including the FoLix laser, work best while living follicles remain, and some causes are quickly resolved once identified. Knowing the cause is what makes the treatment plan actually work.
This article is educational and not a substitute for personalized medical advice.