Perinailitis, also known as perinail furuncle, is a purulent infection of the tissues around the nail caused by a minor local injury, starting with redness, swelling and severe pain on one side of the nail or at the root of the nail, and then gradually becoming purulent and forming a sub nail abscess when it accumulates under the nail, which often becomes chronic inflammation after breaking down due to poor drainage of pus. After perineal infection, purulent infection of the tissues around the nail starts with redness, swelling, and severe pain on one side of the nail or at the nail root, and then gradually becomes pus, and when it accumulates under the nail, it forms an abscess under the nail, and after it breaks down, it often becomes chronic inflammation due to poor drainage of pus. It is often mistaken for having gray nails, so how do you differentiate between nail infections and gray nails? The following is an introduction to the differential diagnosis of perinephritis and gray nails: Diagnosis: The diagnosis can be made based on clinical manifestations. The first manifestation is local redness, swelling, and heat pain. There are usually no systemic symptoms. The infection then spreads to the area around the nail root and under the nail. Differential diagnosis: Perinail infection: A purulent infection of the tissues around the nail that starts with redness and severe pain on one side of the nail or at the nail root, and then gradually becomes purulent and forms an abscess under the nail when it accumulates under the nail, which often becomes chronic inflammation after breaking down due to poor drainage of pus. Tinea capitis: Tinea capitis, commonly known as “gray nail”, is a disease caused by dermatophytes invading the nail plate or under the nail. Nail fungus is a nail infection caused by fungi such as dermatophytes, yeasts, and non-dermatophytes.