1. Androgenetic Alopecia (Genetic Hair Loss)

Androgenetic alopecia, also known as male-pattern or female-pattern baldness, is the most common cause of hair loss. It is hereditary and influenced by hormones called androgens, particularly dihydrotestosterone (DHT). This condition typically results in a receding hairline and thinning at the crown in men, while women experience diffuse thinning across the scalp¹⁻³. 

2. Telogen Effluvium (Stress-Induced Hair Loss)

Telogen effluvium occurs when a significant number of hair follicles prematurely enter the resting (telogen) phase of the hair growth cycle. This condition can be triggered by physical or emotional stressors such as childbirth, surgery, illness, or extreme weight loss. Hair shedding usually begins 2–4 months after the triggering event and can last up to six months⁴⁻⁵. 

3. Hormonal Imbalances

Hormonal fluctuations due to pregnancy, menopause, thyroid disorders, or conditions like polycystic ovary syndrome (PCOS) can disrupt the hair growth cycle. For instance, postpartum women often experience temporary hair shedding due to hormonal changes after childbirth⁶⁻⁷. 

4. Nutritional Deficiencies

A lack of essential nutrients such as iron, zinc, biotin, and vitamin D can lead to hair thinning or shedding. Extreme diets or eating disorders can exacerbate this issue. Ensuring a balanced diet rich in these nutrients is critical for maintaining healthy hair⁸⁻¹⁰. 

5. Autoimmune Conditions

Autoimmune diseases like alopecia areata cause the immune system to attack hair follicles, leading to patchy hair loss on the scalp or body. Severe forms include alopecia totalis (complete scalp hair loss) and alopecia universalis (loss of all body hair)¹¹. 

6. Excessive Hair Care Practices

Frequent use of heat-styling tools, chemical treatments (e.g., bleaching), and tight hairstyles like braids or ponytails can damage hair follicles over time. This may result in traction alopecia—a form of hair loss caused by prolonged tension on the scalp¹²⁻¹³. 

7. Medical Conditions and Medications

Certain medical conditions such as diabetes, lupus, and hypothyroidism can contribute to hair loss. Additionally, medications for cancer (chemotherapy), high blood pressure, depression, or birth control pills may list hair shedding as a side effect¹⁴⁻¹⁵. 

8. Scalp Infections

Fungal infections like tinea capitis (scalp ringworm) or bacterial infections such as folliculitis can weaken hair follicles and lead to temporary or permanent hair loss if untreated¹⁶. 

9. Aging

As part of the natural aging process, many individuals experience gradual thinning of their hair due to a condition called involutional alopecia. This occurs as more follicles shift from the growth (anagen) phase into the resting (telogen) phase over time¹⁷. 

10. Stress and Emotional Factors

Chronic stress increases cortisol levels in the body, which can disrupt the normal functioning of hair follicles. Stress-related conditions like trichotillomania (hair-pulling disorder) also contribute to noticeable hair thinning or bald patches¹⁸.