Final answer:
Photosensitivity is a reaction to UV light intensified by certain substances which can cause adverse skin reactions and immune suppression, but UV light also has beneficial effects like vitamin D production and treatment applications like phototherapy for jaundice.
Step-by-step explanation:
Photosensitivity is a heightened skin reaction to ultraviolet light (UV) due to certain substances, which can lead to adverse effects such as rashes and increased risk of skin cancer. For instance, some photographers develop severe rashes on their hands after being sensitized to film developing chemicals when these are exposed to UV radiation. Sunburn, suppression of the immune system, and the risk of cataracts in the eyes are major concerns associated with UV exposure. Furthermore, while UV-B radiation can lead to skin pigmentation as a defense mechanism, it can also distort the DNA helix, potentially causing cancerous mutations. However, it's important to note that UV exposure has some beneficial effects as well. It triggers the production of vitamin D in the skin, which is essential for bone health. Phototherapy, a treatment that exposes infants with jaundice to UV light, is a therapeutic use of UV that helps reduce toxic levels of bilirubin in the blood.