causes of nails breaking easily but not toenails
4. Health Conditions. If your nails are brittle it may be a sign that you are getting an inadequate amount of oxygen to the feet, which can signal a respiratory issue such as asthma. Psoriasis can mimic the symptoms of a fungal infection in the toenails, causing them to become brittle or fall off. Hyperthyroidism or hypothyroidism can also cause the nails to split or separate easily. Dehydration, alopecia areata or eczema can also cause the nails to become brittle.