Painful lumps under the skin are usually caused by injuries or infections, states MedlinePlus. These lumps include boils, which are caused by infected hair follicles, and carbuncles, which are groups of boils, according to WebMD. Lipomas are soft lumps under the skin that have no known cause, states Mayo Clinic
At first, a boil is pink, tender and swollen, says MedlinePlus. The pain of the boil worsens as it starts to fill up with necrotic matter and is relieved when the boil drains. The boil can drain on its own or might need to be opened, and they are found anywhere on the body.
Lipomas are usually small, soft, doughy lumps under the skin, but they can be painful if they press on nerves or if they are full of blood vessels, says Mayo Clinic.