Have you ever slipped on a pair of second-hand shoes and later noticed a small yellow bump forming on your toe? It can be uncomfortable and a little alarming, especially if you’ve never had one before. In most cases, though, this bump is harmless. It is usually a corn or callus—thickened skin that develops when your body tries to protect itself from repeated friction or pressure. The yellow color comes from layers of dead skin cells, known as keratin, building up over time. While it may look unusual, it’s actually a common response to irritation, particularly when footwear doesn’t fit quite right.

This issue happens more often with pre-owned shoes because shoes naturally mold to the shape of the original owner’s feet. When someone else wears them, the pressure points may no longer line up correctly. Seams, stiff areas, or narrow spots can rub against parts of your toes that aren’t used to that pressure. Repeated friction—especially on the tops or sides of toes—signals your skin to thicken as a defense. Over time, that thickened skin hardens into a raised bump. Hard corns often form in these areas and may develop a small central core that can feel painful when pressed, sometimes described as feeling like stepping on a pebble.

Although corns and calluses are the most common explanation, there are other possibilities to be aware of. Strong friction can sometimes cause blisters, which are fluid-filled and may look yellowish if irritation or infection develops. Fungal infections are another concern with used shoes, as they can carry fungi from the previous wearer. These infections usually show up differently, causing itching, redness, peeling skin, or yellowing and thickening of the toenails rather than a firm, hard bump. Knowing the difference is important, since fungal infections often need specific treatment to clear up completely.

Second-hand shoes come with added risks compared to new ones. Because they’re already broken in for someone else, they often create uneven pressure on your feet. They may also have reduced cushioning or worn-down soles that fail to absorb impact properly. Hygiene is another factor—sweat, bacteria, and fungi can remain in shoes that haven’t been thoroughly cleaned or disinfected. All of these issues increase the chance of irritation, making corns, calluses, or other foot problems more likely to appear after wearing used footwear.

Treating a yellow bump caused by friction is usually straightforward. The first and most important step is to stop wearing the shoes that caused the problem. Switch to well-fitting footwear with a roomy toe box and good support. Soaking your feet in warm, soapy water for 10 to 20 minutes can soften the thickened skin. After soaking, gently use a pumice stone or emery board to smooth the area—never cut the skin yourself. Reducing friction with corn pads, moleskin, or gel toe protectors can help, as can moisturizing creams that contain urea. Over-the-counter treatments with salicylic acid may also help break down thick skin over time.

Prevention is just as important as treatment. If you choose to wear used shoes, clean and disinfect them thoroughly, ideally with antifungal sprays. Always wear socks to reduce friction and moisture, and break shoes in slowly instead of wearing them all day right away. Choose breathable materials and make sure the size truly fits your feet. If the bump becomes painful, red, swollen, produces pus, or doesn’t improve after a couple of weeks, it’s best to see a podiatrist. That yellow bump is your skin’s way of warning you about too much pressure—fixing the fit often solves the problem, and professional care can help if it doesn’t.