Painful Lump Under the Skin: What It Could Be and When to Get It Checked

What does a painful lump under the skin usually mean?

Most tender lumps beneath the skin fall into a few common categories:

Skin abscess (boil). A pocket of pus caused by a bacterial infection, most often Staphylococcus aureus 1Ref 1Stevens DL, Bisno AL, Chambers HF, et al. (2014).Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America.Incision and drainage as the recommended treatment for cutaneous abscesses (boils); classification of skin abscesses and guidance on when antibiotics are needed alongside drainage; management principles for skin infections. These are warm, red, tender, and may come to a visible head. They require drainage — either by a clinician or sometimes on their own — and occasionally antibiotics 1Ref 1Stevens DL, Bisno AL, Chambers HF, et al. (2014).Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America.Incision and drainage as the recommended treatment for cutaneous abscesses (boils); classification of skin abscesses and guidance on when antibiotics are needed alongside drainage; management principles for skin infections. Do not attempt to squeeze or cut one at home 2Ref 2Pastorino A, Tavarez MM (2023).Incision and Drainage.Clinical procedure for abscess incision and drainage; why home drainage of abscesses is discouraged; technique overview and indications.

Inflamed or infected cyst. Epidermoid (skin) cysts are common sac-like structures under the skin. They are usually painless until they become infected or rupture, at which point they become red, warm, and quite tender. A clinician can drain or surgically remove them.

Reactive lymph node. Lymph nodes are small immune-system structures in the neck, armpits, groin, and elsewhere. When your body fights a nearby infection, the local node can swell and become tender. This is usually temporary and resolves as the infection clears.

Lipoma. These are benign fatty growths beneath the skin — almost always soft, movable, and painless. They can become tender if they press on a nerve or are in a location subject to friction. A suddenly painful lipoma should be re-evaluated.

Ingrown hair or folliculitis. Hair trapped beneath the skin can cause a small, tender red lump, especially in shaved or friction-prone areas.

Less common causes worth knowing

A clinician will also consider less common causes based on location, characteristics, and your history:

• Ganglion cyst: A fluid-filled sac most common near joints — wrists, fingers, feet — that can become painful with use.
• Hidradenitis suppurativa (HS): A chronic inflammatory skin condition causing recurring painful lumps in areas where skin rubs together — armpits, groin, under the breasts 3Ref 3Krueger JG, Frew J, Jemec GBE, et al. (2024).Hidradenitis suppurativa: new insights into disease mechanisms and an evolving treatment landscape.Hidradenitis suppurativa as a chronic inflammatory skin condition causing recurring painful lumps in intertriginous areas; its frequent misdiagnosis as recurrent boils; the importance of dermatologist evaluation. HS is frequently misdiagnosed as recurring boils for months or years before a correct diagnosis is made; early dermatology referral matters 3Ref 3Krueger JG, Frew J, Jemec GBE, et al. (2024).Hidradenitis suppurativa: new insights into disease mechanisms and an evolving treatment landscape.Hidradenitis suppurativa as a chronic inflammatory skin condition causing recurring painful lumps in intertriginous areas; its frequent misdiagnosis as recurrent boils; the importance of dermatologist evaluation.
• Enlarged lymph node from a distant infection or illness — sometimes the source is not immediately obvious.

In rare cases, a lymph node — especially one accompanied by systemic symptoms — may signal something that requires further workup. This is why persistent or worsening lumps should be seen by a clinician even when the cause seems straightforward.

What happens at a clinician visit?

A clinician will ask how long the lump has been present, whether it is changing, any associated symptoms (fever, weight changes, skin changes), and your medical history. They will feel the lump to assess its size, consistency, mobility, and whether the overlying skin is involved. For most benign lumps this is all that is needed to make a working diagnosis.

If infection is suspected, needle aspiration or incision and drainage may be performed — this is both diagnostic and therapeutic. If the diagnosis is uncertain, an ultrasound can distinguish a fluid-filled cyst from a solid mass. In unusual cases, a biopsy or blood work (complete blood count, inflammatory markers) may follow.

Factors that change what a lump might mean

Location matters a great deal. A lump in the breast or testicular area warrants timely evaluation regardless of whether it hurts. A lump in the neck, armpit, or groin — particularly with systemic symptoms — raises different concerns than one on the back.

Immune status. People with diabetes, HIV, or on immunosuppressive medications are more susceptible to skin infections and may have more serious presentations that need faster treatment.

Age. Lipomas and cysts are more common in middle-aged adults. A clinician weighs age when assessing lymph nodes that are not clearly reactive.

Recent travel or animal exposure. Some infections that cause skin lumps or swollen lymph nodes are linked to animal bites, scratches, or travel — cat-scratch disease is one example.