That sudden yellow bump after wearing second-hand shoes is usually your skin’s alarm system, not a medical disaster. Most of the time, it’s a corn or callus: thickened skin formed where your toe has been repeatedly squeezed or rubbed inside a shoe shaped for someone else’s foot. The pressure focuses on one small area, and your body responds by building a tiny “shield” of hard skin that looks yellow and feels like a pebble underfoot.

The fix is almost always simple: stop wearing the offending shoes, switch to well-fitted footwear with room around the toes, and gently soften the thick skin with warm soaks, a pumice stone, and moisturizer. Pads or gel protectors reduce friction while it heals. If the bump becomes very painful, red, swollen, or shows signs of infection, a podiatrist can safely remove the thickened skin and check for deeper problems, ensuring you walk away comfortable and reassured.