The causes for a hard lump on your earlobe vary, ranging from infections to tumors. The rate at which they grow and the amount of pain experienced depend on the cause, according to Health Grades.
Osteomas and exostoses are two types of tumors that appear as hard lumps on your earlobe (and elsewhere on your ear). Pain behind the ear as well as a hard lump on the ear lobe, can be caused by mastoiditis, an infection that targets the mastoid bone. An injury to the ear that causes blood to gather in the tissues is also a possible cause, as stated by Health Grades.