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

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

Surgical excision - Even if you keep squeezing what comes out from inside, it usually recurs. Therefore, surgical resection may be required. Painful lesions and suspected infection should be treated with antibiotics.

Treatment ― OTC Drugs
Frequent touching of the affected area may cause it to become inflamed. Most inflamed lesions larger than 1 cm usually require surgical treatment in the hospital. If small lesions are inflamed, you may try to use OTC antibiotics. Do not use a steroid ointment for the epidermal cyst.
  • 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 the presence of a central discharge hole, such as a black dot in the middle.
  • Typical inflammed 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, Epidermal cyst often have a palpable lump.
  • Inflamed thyroglossal cyst
References Minimally Invasive Excision of Epidermal Cysts through a Small Hole Made by a CO2 Laser 24511501 
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 
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 
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 
On radiology, they have round to oval structure, well-circumscribed, avascular mass; restricted diffusion is typical.