11 Bad Habits That Make Your Hair Thinner (http://health.yahoo.net/articles/beauty/11-bad-habits-make-your-hair-thinner)
1. Taking steamy showers
2. Using hot styling tools
3. Crash dieting
4. Mishandling wet hair
5. Wearing tight hairstyles
6. Using long-lasting hold styling products
7. Taking oral birth control pills
8. Scratching your head
9. Soaking up the sun
10. Not washing hair often enough
11. Taking certain medications
All of these are discussed more in the article.