There can be several causes for a localized swelling in the arm, such as epidermal inclusion cyst, infected lipoma, abscess, boil/furuncle or fibroma. It would be difficult to diagnose without an examination.
Lipomas are the most common soft tissue tumors and are slow-growing, benign in nature. They contain fat which forms lobulated soft masses enclosed by a thin fibrous capsule. Lipomas occur in 1% of the population. They presumably arise from fat that may occur in the back, hips, neck or other parts in adults. An epidermal inclusion cyst is a sac like structure with skin debris inside. These types of swellings are usually not malignant.
You should consult a surgeon for a proper diagnosis and treatment. The diagnosis is through physical findings. Sometimes a needle biopsy or a CT scan may be done to confirm the diagnosis or rule out any malignant changes. The therapy depends on the location and diagnosis of the swelling. Most of these are small subcutaneous in location and are removed for cosmetic reasons.
Hope it helps
Thank you very much. Yes it helps - but worries me a little bit. I will go and consult very soon.