There are lots of reasons for brittle nails, such as growing age or polishing the nails frequently. In the cold temperature, they may occur due to dryness. They are also a sign of serious health issues such as anemia, nutritional deficiency, infection, and thyroid disease. Before heading to a doctor, you can use nail hardening products and also decrease the number of manicures. While doing the housework or washing the dishes, wear gloves.