Understanding Hair Loss: Common Causes
Hair loss can be distressing, but it’s often a sign that something in the body is out of balance. Hair follicles are susceptible to hormones, nutrients, and stress, so even small changes can affect hair growth. Understanding the causes and the biology behind them can help you address hair loss effectively.
1. Androgen Excess (Women and Men)
What it is: Androgens are hormones like testosterone and DHT that regulate hair growth patterns. Too much androgen can cause hair thinning and shedding.
How it affects hair:
In women, excess androgens (common in conditions like PCOS and menopause) can lead to hair thinning at the crown and frontal scalp.
In men, higher sensitivity to DHT can cause male pattern baldness, usually starting at the temples and crown.
Pathophysiology: Excess androgens bind to hair follicle receptors, shortening the growth (anagen) phase and miniaturizing hair follicles. Over time, this produces thinner, shorter hairs, and eventually, some follicles may stop producing hair entirely.
2. Thyroid Imbalance
What it is: The thyroid gland produces hormones that regulate metabolism. Both hypothyroidism (low thyroid hormone) and hyperthyroidism (high thyroid hormone) can cause hair loss.
How it affects hair:
Hair may become dry, brittle, or thin.
Diffuse shedding across the scalp is common, along with thinning of the outer 1/3 of the eyebrows.
Pathophysiology: Thyroid hormones regulate hair follicle cycling. Imbalances disrupt the normal cycle, often pushing hairs prematurely into the shedding (telogen) phase, resulting in diffuse hair loss.
3. Nutrient Deficiencies
Several nutrients are critical for healthy hair growth:
Low Iron
Why it matters: Iron is essential for oxygen delivery to cells, including hair follicles. Low iron can starve follicles of energy.
Pathophysiology: Hair follicles prematurely enter a resting phase, leading to diffuse shedding.
Low Zinc
Why it matters: Zinc supports cell division and protein synthesis. Deficiency can cause weak, brittle hair and slow regrowth.
Pathophysiology: Zinc deficiency disrupts hair follicle cell proliferation, weakening the hair shaft.
Low Protein
Why it matters: Hair is made of keratin, a protein. Low dietary protein reduces the building blocks for hair growth.
Pathophysiology: Hair growth slows, follicles shrink, and hair becomes thin and fragile.
4. Alopecia Areata
What it is: Alopecia areata is an autoimmune condition where the body mistakenly attacks hair follicles.
How it affects hair:
Causes patchy hair loss on the scalp or other body areas.
Hair can regrow, but may fall out again.
Pathophysiology: Immune cells (T cells) target hair follicles, disrupting the normal growth cycle. This inflammatory attack forces hairs into the shedding (telogen) phase prematurely.
5. Telogen Effluvium
What it is: Telogen effluvium is diffuse hair shedding often triggered by stress, a major illness, or toxin exposure.
How it affects hair:
Hair falls out in large amounts, usually 2–3 months after a trigger.
Scalp may look thinner, but hair usually regrows once the trigger is removed.
Pathophysiology: Hair follicles are pushed prematurely into the telogen (resting) phase. A key factor is oxidative stress and low levels of antioxidants, such as glutathione, which help protect follicle cells from damage.
How These Causes Connect
Despite different triggers, most hair loss involves a disruption of the hair growth cycle:
Anagen phase – active growth.
Catagen phase – transition.
Telogen phase – resting/shedding.
Hormonal imbalances, nutrient deficiencies, immune activation, and oxidative stress all shorten the anagen phase or push hairs into telogen prematurely, leading to thinning and shedding.
Practical Takeaways
Hair loss is often multifactorial—more than one cause may contribute.
Evaluating hormones, thyroid function, iron, zinc, protein intake, and oxidative stress under the supervision of a healthcare provider can guide targeted interventions.
Supporting overall health, including stress management, nutrition, and antioxidant support, helps hair follicles return to a healthy growth cycle.
Disclaimer: This information is for educational purposes only and is not intended to provide or replace medical advice, diagnosis, or treatment. Always consult your qualified healthcare provider for individualized recommendations.