Why do fingernails split horizontally?

Fingernails can split horizontally due to a variety of factors, including dehydration, trauma, or excessive exposure to water and chemicals. Nutritional deficiencies, particularly in biotin or protein, can also weaken nails and lead to splitting. Additionally, underlying health conditions, such as thyroid disorders or fungal infections, may contribute to this issue. Proper nail care, including moisturizing and avoiding harsh substances, can help prevent horizontal splits.