What are four factors that can lead to hair thinning other than nutritional or circulatory factors?

1. Hormonal changes: Changes in hormone levels, such as those that occur during pregnancy, menopause, or with certain medical conditions (e.g., thyroid issues), can lead to hair thinning.

2. Genetics: Some people are more likely to develop hair thinning due to genetics. Certain genes may make individuals more susceptible to the effects of hormones, such as dihydrotestosterone (DHT), which can contribute to hair loss.

3. Medications: Certain medications, including chemotherapy drugs, antidepressants, and some hormonal treatments, can cause hair thinning as a side effect.

4. Stress: Severe or chronic stress can lead to temporary hair thinning. This is because stress can affect the body's production of hormones, which can in turn impact hair growth.