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Quite commonly people will develop sebaceous cysts on their head and neck. A sebaceous (or epidermoid) cyst is a noncancerous swelling under the skin. It is lined by packed outer skin cells. The cyst itself is filled with oil or dead cells. Under certain conditions such as stress, increased activity, mechanical irritation, diabetes, or other concurrent illness these cysts may enlarge and become somewhat tender. On occasion, these cysts will be drained by the physician and antibiotics will be prescribed. Warm moist compresses will commonly help bring these cysts “to a head” and help them drain. It is not uncommon for these cysts to increase and decrease in size particularly when there is increased activity and/or sweating. Sebaceous cysts are commonly present in patients with cystic acne. Another possibility is a swollen lymph node.
I would have it looked at by your doctor
Lori