A large, raised, swollen skin lesion with a central opening and yellowish or greenish material may indicate an infected epidermoid cyst, skin abscess, or boil. These conditions can cause redness, tenderness, pressure, and drainage. However, appearance alone cannot confirm the diagnosis, and other skin conditions may look similar. A healthcare professional should examine any large, open, or worsening lesion.

An epidermoid cyst forms when skin cells become trapped beneath the surface, creating a pocket filled with keratin, a thick substance that can resemble pus. If the cyst ruptures or becomes inflamed, it may swell, become painful, and release thick or unpleasant-smelling material. A skin abscess or boil is a collection of pus, often caused by bacteria entering through damaged skin or a hair follicle. The surrounding area may feel warm and become increasingly tender.

Treatment depends on the cause and severity. A medical professional may perform incision and drainage to remove accumulated pus and relieve pressure. Antibiotics may be prescribed if there is spreading infection or another medical reason to use them, although they are not necessary for every abscess. If an epidermoid cyst repeatedly returns, removing the entire cyst capsule may help prevent recurrence.

Until the lesion is examined, avoid squeezing, cutting, or draining it yourself. Keep it clean and covered with a sterile dressing. Seek prompt medical attention, particularly if it is large or worsening. Fever, chills, spreading redness, increasing pain, or rapidly growing swelling require urgent assessment. Early treatment can reduce complications and help the wound heal safely.