Painful bumps under the skin can feel tender and uncomfortable. They often come from inflammation, infections, cysts, or other issues deep in the tissue.
One common cause is erythema nodosum. This happens when the body’s immune system reacts strongly to something like an infection, certain drugs, or even pregnancy. It leads to red, painful lumps on the shins or arms from swollen fat under the skin.
Infections play a big role too. Bacteria can form abscesses, which are pus-filled pockets that hurt a lot. These might start from a small cut or hair follicle that gets infected. Viruses, fungi, or even tick bites can trigger similar bumps.
Cysts are another frequent reason. Epidermoid cysts grow when skin cells get trapped under the surface and fill with thick fluid. They can become painful if they get inflamed or infected. These show up on the face, scalp, or back.
Swollen lymph nodes often cause thigh or groin lumps. Your body swells these nodes to fight nearby infections from bacteria or viruses. The pain comes from the pressure as they enlarge.
Benign tumors like angiolipomas or neuromas can also hurt. Angiolipomas mix fat and blood vessels, feeling tender on the arms or trunk. Neuromas form from nerve tissue after injury and throb when pressed.
Less common but serious causes include autoimmune conditions or cancers. Things like lymphoma might create firm, red nodules that grow slowly. Panniculitis-like lymphomas mimic fat inflammation but involve abnormal cells.
Trauma or injury can lead to these bumps. A bruise or repeated friction might cause deeper swelling or even calcinosis, where calcium deposits form in damaged tissue.
Allergic reactions or drugs, such as birth control pills or antibiotics, sometimes spark painful nodules. Metabolic issues or poor circulation can contribute in rare cases.
If you notice these bumps, especially if they grow, leak pus, or come with fever, see a doctor. They can check for the exact cause with an exam or tests.
Sources
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https://www.ummhealth.org/health-library/epidermoid-cysts-of-the-skin
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