What causes spurs on your heels. and why do they hurt?

Plantar fasciitis: The "spur" comes from bone formation in the soft tissue attached to the heel, the plantar fascia. This is due to degeneration of the tissue as well as chronic low grade inflammation. The spur itself is not felt to be the primary cause of the pain. The pain comes from the soft tissue. Time and plantar fascia stretching exercise can help. Injections may have some benefit. Surgery is rarely needed.

Don't blame the spur: Heel spurs on the bottom of the foot occur where one of the foot muscles arise from the heel bone. It is likely more a sign of disease then the actual problem. Often the body puts calcium/bone in injured or degenerated areas.