Why does scalp cyst cause skin lumps?

A pilar cyst, also called a trichilemmal cyst, develops from the outer part of a hair follicle. The cyst wall produces and contains keratin, a tough protein found in hair and the outer layer of skin. As material collects inside the sac, it creates a smooth, firm or rubbery bump under the scalp.

Many pilar cysts are covered by normal-looking skin and move slightly when pressed. They may be solitary or occur in several places, and a family tendency can make them more likely. A scalp lump can have other causes, so its appearance alone cannot confirm a cyst.

Do not squeeze, pierce or cut the lump at home. This can irritate the cyst, introduce infection or leave material behind. Protect it from repeated combing, tight headwear and knocks, and arrange a clinical assessment if you are unsure what it is.

If a pilar cyst is troublesome, repeatedly inflamed or catches on hair care, a clinician can discuss removal of the cyst and its wall. An inflamed cyst may need a different approach, so treatment is chosen after examination.

Seek prompt care if the lump becomes rapidly larger, hot, red, very painful or starts draining. Fever, spreading redness or swollen glands may indicate infection. A hard, fixed or persistently changing scalp lump also deserves examination rather than home treatment.

Does this lump have features of a pilar cyst or another scalp growth? Is removal appropriate if it catches on my comb? What should I do if it becomes tender, red or starts to drain?