hi thanks for posting your query on healthcare magic what you are mentioning is most probably a sebaceous cyst found incidentally and correlated with trauma . A sebaceous cyst is also known as a keratin or epidermal cyst and is a closed sac under the skin filled with a cheese-like or oily material known as sebum . Sebaceous cysts most often arise from swollen hair follicles. Skin trauma can also induce a cyst to form. A sac of cells is created into which a protein called keratin is secreted. These cysts are usually found on the face, neck, and trunk. They are usually slow- growing, painless, freely movable lumps beneath and adhered to the skin. Occasionally, however, a cyst will become inflamed and tender. The main symptom is usually a small, non-painful lump beneath the skin. If the lump becomes infected or inflammed, other symptoms may include: Skin redness Tender or sore skin Warm skin in the affected area Grayish-white, cheesy, sebum material may come out . The cyst almost always has a small punctum ( black dot ) over the cyst. The sebaceous cyst are usually not dangerous and are ignored till complicate by secondary infection where they may form abscesses and burst to drain purulent collection. It is advisable to get it excised under local anesthesia before this stage develops. i hope i have answered to all your queries .In case of any further doubts Kindly post again God Bless