What should you know about a blue bump on skin?

Blue or blue-purple colour can come from blood beneath the skin after an injury, blood vessels close to the surface, or pigment deeper in the skin. A raised spot may also be an irritated follicle, bite, inflamed cyst, or another growth. Colour alone cannot identify the cause. Note whether it is soft or firm, tender or itchy, mobile or fixed, and whether it appeared after pressure, shaving, or a knock. A cluster of small bumps may fit a rash; one persistent changing lesion deserves a closer look.

Take a clear photograph beside a familiar object for scale and record when you first noticed the bump. Avoid squeezing, piercing, or repeatedly rubbing it. If it followed a minor knock, gentle cold compresses wrapped in cloth may reduce discomfort during the first day. Use bland skin care and protect the area from sun while it settles. A clinician can examine persistent bumps and may discuss options such as cryotherapy for a suitable lesion; antihistamine treatment may help itch when an allergic process is suspected.

Arrange a dermatology assessment if the bump persists, enlarges, becomes firmer, bleeds, crusts, ulcerates, or develops an uneven outline or new colours. Seek prompt care for spreading redness, warmth, pus, severe pain, fever, or rapid swelling. A blue mark after a clear injury that gradually fades is less concerning, but unexplained or repeatedly returning lesions should still be checked.

Could this be a bruise, vessel, inflamed follicle, cyst, or another type of lesion? Does its texture or location suggest a particular cause? Would monitoring, dermoscopy, treatment, or a sample be appropriate? What changes should prompt an earlier review?