Which of the following is a common symptom of onychomycosis?

Onychomycosis, also known as a fungal nail infection, is characterized primarily by specific changes in the appearance of the nails. The thickening and discoloration of the nail is a hallmark symptom of this condition. These changes often include yellow or white patches or streaks on the nail, which can progress to a more severe state where the nail becomes thickened, brittle, and even separates from the nail bed in advanced cases.

This symptom helps differentiate onychomycosis from other nail disorders that may present differently. For instance, while severe pain around the nail could suggest various issues, it is not a common symptom associated with onychomycosis itself. Similarly, a foul odor might be present in other types of infections but is not specifically tied to onychomycosis. Heightened sensitivity to touch may also indicate other medical concerns but is not typically a symptom seen with fungal infections of the nail. Thus, the correct identification of thickening and discoloration as a primary symptom focuses attention on the characteristic alterations that help in the diagnosis of onychomycosis.