Dark lines beneath the nail should be carefully evaluated.While some pigmentation is harmless, especially in individuals with darker skin tones, a dark vertical streak can sometimes indicate subungual melanoma, a serious form of skin cancer. If a dark stripe appears suddenly, changes shape, or extends into the surrounding skin, a dermatologist should examine it promptly.Clubbing of the nails is another important sign.This condition causes the fingertips to enlarge and the nails to curve downward around the fingertips. Clubbing develops gradually and is often associated with chronic lung diseases, heart disease, inflammatory bowel disease, or certain cancers.It reflects long-term low oxygen levels in the blood.Horizontal ridges across the nails, known as Beau’s lines, may appear after severe illness, high fever, major stress, surgery, or chemotherapy.These ridges form when nail growth temporarily stops due to systemic shock or metabolic stress.The depth of the ridge can sometimes reflect the severity of the event.Vertical ridges, on the other hand, are common with aging and usually harmless. However, if they are accompanied by splitting or discoloration, they could signal nutritional deficiencies, particularly low levels of magnesium or vitamin B12.Pitting of the nails, which appears as small dents or depressions in the nail surface, is often associated with autoimmune conditions such as psoriasis.Psoriasis affects skin cell turnover, including in the nail matrix. Nail pitting may also occur in alopecia areata or other inflammatory disorders.
