Big hard lump under the skin on the buttock

Possible explanations include an inflamed hair follicle or boil, a blocked skin cyst, a fatty lump, scar tissue, or a reaction at an injection site. Examination is needed to distinguish these because firmness alone does not identify the cause.

A warm, tender lump that becomes red or forms pus can fit a boil or abscess. A cyst may feel smooth and rounded, sometimes with a small central opening, while a fatty lump is often softer and moves slightly under the fingers. Repeated pressure, previous injury, surgery, or an injection can also leave a firm area.

A clinician will consider its depth, mobility, skin colour, tenderness, growth, and any drainage. A persistent lump that is attached to deeper tissue or accompanied by skin breakdown deserves prompt evaluation, even when it does not hurt.

Do not squeeze, puncture, or cut the lump; this can push infection deeper and cause bleeding or scarring. Reduce friction and direct pressure, keep the area clean and dry, and use a warm compress for a tender superficial bump. Note whether its size, colour, pain, or discharge changes.

Arrange a routine appointment if the cause is unclear or the lump remains. Depending on the examination, a clinician may recommend imaging, drainage, removal, or treatment aimed at inflammation. Antibiotics are useful only when a bacterial infection is suspected.

Seek urgent care for rapidly spreading redness, severe or escalating pain, fever, chills, extensive swelling, foul drainage, darkening skin, or feeling generally unwell. Prompt care is also sensible if diabetes, reduced immunity, or medicines that suppress immunity could make an infection harder to control.

Book an assessment for a lump that grows, feels fixed, repeatedly returns, bleeds, ulcerates, changes the overlying skin, or interferes with sitting or walking. These features do not establish a diagnosis, but they change how quickly the area should be examined.

Ask whether the lump appears to come from skin, fat, or deeper tissue; whether imaging or a sample would clarify it; and which changes should trigger urgent review. Mention recent injections, injuries, drainage, previous similar lumps, and medicines that affect immunity or bleeding.