Depends. Sunburn symptoms usually start about 4 hours after sun exposure, worsen in 24–36 hours, and resolve in 3–5 days. However, even after sunburn fades, it may still leave a mark on your skin, resulting in photoaging or even serious skin conditions such as cancer. Depends. Sunburn symptoms usually start about 4 hours after sun exposure, worsen in 24–36 hours, and resolve in 3–5 days. However, even after sunburn fades, it may still leave a mark on your skin, resulting in photoaging or even serious skin conditions such as cancer.