Why does nail turn brittle?

1. Chemical damage: 

1. A) Regular use of nail polish, nail polish remover, acrylic and gel nails would gradually make nail brittle.
2. B) Regular use of harsh soap and detergents

1. Hormonal imbalance Nutritional deficiency: Lack of essential nutrients like biotin, iron calcium etc. 
2.  Thyroid abnormalities (both hyper and hypothyroid) would lead to brittle nails.
3. Others:  Excessive wetting of hands 

HOW CAN ONE TREAT BRITTLE NAILS?

1. Reduce the frequency of acrylic and gel nail manicures: Lesser the chemical exposure the better it is.
2. Use mild soaps: Use SLS free soaps for hand wash and bathing. Dove or Cetaphil cleansing lotion are good options. Ditch soaps like Dettol, lux , lifeboy etc. for they have a harmful chemical SLS. 
3. Get thyroid levels checked: In case found disrupted, consult a physician to rectify the   same.