Final answer:
A first-degree burn affects only the epidermis, the outer layer of skin. It can be caused by excessive sun exposure and usually heals on its own within a few days.
Step-by-step explanation:
A first-degree burn is a superficial burn that affects only the epidermis, the outer layer of skin. It is typically caused by exposure to sun or tanning lamps.
Symptoms include redness, pain, and swelling, but these burns usually heal on their own within a few days.