Final answer:
A sunburn is caused by exceeding the individual threshold dose of UV-B and UV-C radiation that damages the skin's epidermis. Severe or repeated sunburns can lead to an increased risk of skin cancer. Using sunscreens can help protect the skin from immediate and long-term UV-induced damage.
Step-by-step explanation:
The threshold dose that can cause sunburn is the amount of UV-B and UV-C radiation exposure that leads to the damage of the epidermis, the outer layer of the skin. While sunlight is beneficial for vitamin D synthesis, overexposure to UV rays, specifically UV-B with wavelengths of 280-320 nm, can damage the skin and lead to sunburn. Sunburn is a clear indication of skin damage, and experiencing severe burns, particularly ones that cause blistering, significantly increases the risk of developing skin cancer later in life. The body's natural defense against UV radiation is the tanning response, where it produces pigments to shield the living cells under the skin layers. Effective sunscreens provide protection against both immediate and long-term skin damage.