I have a few hard lumps on my head just below the service. at first there was just one now there are five . they are very hard but do not move . start small grow to about hr size of a pea.

If : If the scalp moves freely over these lumps, and they feel hard like bone, they are likely to be osteomas which are benign and don't typically need treatment unless symptomatic. In some rare cases, they may be related to a systemic disorder ( such as gardner's syndrome associated with colonic polyps). My best recommendation is have someone check these out to make a proper diagnosis and hopefully reassure you there is nothing to worry about.

Simple vs serious: Our bodies always have things that grow and change. Skin, fat, muscle, lymph nodes, bones, can change shape, get larger, more prominent due to many factors. The vast majority are not cancer but simply unusual growths like fatty tumors, cysts, skin tags, moles, etc. Most cause no symptoms and can be watched. If they cause symptoms or change colors, bleed, bruise or hurt, then see your doctor.