If you’ve noticed a bump on the back of your heel, the most likely explanation (although certainly not the only possible diagnosis) is Achilles tendinitis.
Achilles tendinitis is typically the result of chronic, repetitive strain on the Achilles tendon that eventually causes the tendon fibers to tear or degenerate. This leads to thickening and swelling in the tendon, which often produces a noticeable “bump” along the back of the heel that may be extremely tender when pressed.
Often, the first sign of Achilles tendinitis is mild aching in the back of the tendon, above the heel, especially after periods of activity. However, as the condition worsens you may start to feel more severe pain, swelling, tenderness, and stiffness that doesn’t always go away with rest. Eventually, the tendon may completely rupture, so it’s critical you get the care you need sooner rather than later.
Another possible explanation for a bump at the back of the heel is Haglund’s deformity. This condition is thought to be a natural reaction to extended irritation and inflammation in the bursa sac located along the back of your heel. Your body attempts to deal with the trauma by leaving bony deposits on the end of the heel bone, creating a very hard bump that can cause further discomfort. If you regularly wear hard-backed footwear, such as pumps or ice skates, you may be more likely to develop Haglund’s deformity.