Thinning hair is pretty common among men and women based on many different factors of that persons life, so below I have listed some reason why your hair may be thinning.
1. Heredity- This one is pretty self explanatory, and has nothing to do with what your "doing". Normally in families thinning hair is common in either the women, men or both. Which means if your grandmother has super thin edges, the most likely your mom will get super thin edges and so will you.
2. Hormonal changes- This can be anything from post partum shedding to starting new medication. Your hormones can be pretty sensitive sometimes and if they are triggered some side effects could include thinning hair or hair loss.
3. Tight hairstyles- When picking any hairstyle no matter how cute it is you want to make sure that its not pulling on your scalp and edges super tight. Continuous pulling on your scalp and edges will result in that hair becoming thinner and thinner and eventually falling out.
3. Aging- As we age it is pretty common to start getting thin spots (mainly in the top of your head). To "reverse" this you want to make sure that you're actually taking care of your hair from the inside out. Making sure your drinking your water and making sure that you have a hair routine down packed that is going to encourage hair growth and health.