Factor

Effect on Hair Growth

Beta-fibroblast growth factor
Platelet-derived growth factor

Potentiate growth of dermal papillae.

Transforming growth factor beta

Inhibits follicle proliferation, if induced by mitogens.

Interleukin-1 alpha

Inhibits growth of hair and follicle.

Epidermal growth factor

Stimulates growth.

Fibroblast growth factor-5

Inhibits growth.

Keratinocyte growth factor

Stimulates growth; induces keratinization.

Insulin-like growth factor-1

Accelerates growth of hair and follicle.

Skin damage (e.g., cut, scrape, burn, irritation)

Forces telogen to anagen (well-illustrated in rodent models).

Allergens (e.g., food)

Major changes in the skin, including hair loss.

Malnutrition

Protein/calorie deficiencies inhibit hair growth.

Fungal infection

Inhibits growth; hair may fall out.

Hypothyroidism

Diminution of eyebrows.

Viral agents (e.g, HIV virus)

Hair loss in patches.