Epidermal cysthttps://en.wikipedia.org/wiki/Epidermoid_cyst
Epidermal cyst is the most common benign cyst usually found on the skin. An epidermal cyst may have no symptoms, or it may be painful when touched. It can release macerated keratin.

Epidermal cysts account for approximately 85–95% of all excised cysts, and malignant transformation is exceedingly rare. Cysts can be removed by excision.

○ Treatment
Surgical excision – Even if you keep squeezing the contents, the cyst usually recurs. Therefore, surgical removal may be required. Painful lesions and suspected infection should be treated with antibiotics.

○ Treatment ― OTC Drugs
Frequent touching of the affected area may cause inflammation. Most inflamed lesions larger than 1 cm usually require surgical treatment in a hospital. If a small lesion is inflamed, you may try an OTC antibiotic. Do not use a steroid ointment for an epidermal cyst.
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  • If a small lump that usually persists suddenly becomes inflamed, it may be suspected as an epidermal cyst.
  • This case can be difficult to differentiate from a common abscess.
  • A characteristic feature of epidermal cysts is a central opening, often seen as a black dot in the middle.
  • Typical inflamed epidermal cyst — a black opening in the center.
  • It appears as an old, slowly growing lump, and when squeezed, keratin material may be released.
  • Epidermal cyst is a lump filled with keratin.
  • Small lesions may look like abscesses, but unlike abscesses, an Epidermal cyst often has a palpable lump.
  • Inflamed thyroglossal cyst
References Minimally Invasive Excision of Epidermal Cysts through a Small Hole Made by a CO2 Laser 24511501 
NIH
To improve the cosmetic results of removing epidermal cysts, minimally invasive methods have been proposed. We proposed a new minimally invasive method that completely removes a cyst through a small hole made by a CO2 laser. Twenty-five patients with epidermal cysts, which were 0.5 to 1.5 cm in diameter, non-inflamed, and freely movable, were treated. All of the patients were satisfied with the cosmetic results. This method is simple and results in minimal scarring and low recurrence rates without complications.
 Epidermal Inclusion Cyst 30335343 
NIH
Epidermal inclusion cysts are the most common cutaneous cysts and can occur anywhere on the body. These cysts typically present as fluctuant nodules under the surface of the skin, often with visible central puncta. These cysts often become painful to the patient and may present as a fluctuant filled nodule below the patient's skin.
 Epidermoid Cyst 29763149 
NIH
Epidermoid cysts, also known as a sebaceous cysts, are encapsulated subepidermal nodules filled with keratin. Most commonly located on the face, neck, and trunk.
 Overview of epidermoid cyst 31516916 
NIH
On radiology, they have round to oval structure, well-circumscribed, avascular mass; restricted diffusion is typical.