According to Dr. Standley, flat nails may indicate Raynaud's disease, a condition that most commonly affects women ages 18 through 30. Other changes in nail shape and appearance, such as spooning, pitting, thickening or thinning of the nail plate, white lines under the nail, ridges, yellow or bluish hue and wide nails, may also indicate a new or worsening health condition and require evaluation by a health professional.
Raynaud's disease causes some areas of the body to feel numb or cold during cool weather or stressful situations, says Mayo Clinic. The affected areas usually include fingers, toes, nose and ears, but this disease may affect other areas as well, such as the nipples and lips. The condition occurs when small arteries become narrow thus limiting the amount of blood supplied to certain areas.
This disease is more common in people who live in cooler climates. Symptoms include cold fingers and toes, numb or prickly feelings in the affected areas, and changes in skin color says Mayo Clinic. The symptoms appear in waves and can last for mere minutes or several hours. While the condition is not dangerous and normally does not require medical intervention, it can be annoying. Any signs of infection or sores merit investigation as well.