Hair Loss

The Hair Growth Cycle

The three main phases of the hair cycle are:

Anagen: Actively growing hair, most of them.

Catagen: In-between phase of 2–3 weeks when growth stops and the follicle shrinks, 1–3% of hairs.

Telogen: Resting phase for 1–4 months, up to 10% of hairs in a normal scalp.

Hair length depends on the duration of anagen. Short hairs (eyelashes, eyebrows, hair on arms and legs) have a short anagen phase of around one month. Anagen lasts up to 6 years or longer in scalp hair.

Hair loss can result from various factors, including:

1. Pattern Hair Loss (Androgenetic Alopecia – most common): Affects 50% of people by the age of 50. In males, it affects the vertex and temporal scalp. In females, it tends to affect the anterior scalp or the central part line. Pattern hair loss is due to genetic programming or hormonal influences (testosterone).
2. Decreased Hair Growth (Anagen Hair Loss): Caused by autoimmune diseases like alopecia areata, medications (especially chemotherapy drugs), and congenital conditions like loose anagen syndrome (rare).
3. Increased Hair Shedding (Telogen Hair Loss): Caused by events such as physical illnesses or psychological stress, usually after medications like oral contraceptives and oral isotretinoin (Vitamin A).
4. Dermatological Diseases: Conditions like alopecia areata, tinea capitis, seborrheic dermatitis (fungal infection), and severe skin diseases like psoriasis and cutaneous lupus.
5. Systemic Diseases: Iron deficiency, folate, Vitamin B12, Vitamin C, and D deficiencies, thyroid hormone deficiency, lupus, syphilis, or severe acute or chronic diseases.
6. Scarring Alopecia: Due to injury to the dermis or subcutaneous tissue where the hair follicles are resulting in a bald patch. Causes include trauma from injury, surgery, radiation, or traction (most commonly seen in very tight curls), infections, or inflammatory skin diseases like discoid lupus erythematosus.
7. Hair Shaft Abnormalities (Rare): Inherited or acquired defects in the hair shaft structure.