After common warts turn black, they generally fall off within about a week. Common warts, also known as verruca vulgaris, are primarily caused by infection with the human papillomavirus, typically by the type 2 HPV virus. The occurrence of common warts is associated with numerous factors; they often arise when the body's immune system is weakened, or when warts already present are frequently scratched, which can lead to inoculation infection. Common warts can occur on various parts of the body and are commonly found on the hands. The hands are particularly susceptible if they are kept in water for prolonged periods, which can easily trigger the appearance of common warts. Typical lesions of common warts are pea-sized or larger, gray-brown or brown papules with a rough surface and hard texture, forming papillomatous proliferations. If common warts appear, treatment options such as liquid nitrogen freezing or carbon dioxide laser treatment are available at hospitals.