Unlike phototoxic reactions which resemble exaggerated sunburns, photoallergic reactions can cause intense itching and can lead to thickening of the skin. Phytophotodermatitis: UV radiation induces inflammation of the skin after contact with certain plants (including limes, celery, and meadow grass). Causes pain, redness, and blistering of the skin in the distribution of plant exposure. Polymorphic light eruption: Recurrent abnormal reaction to UVR. It can present in various ways including pink-to-red bumps, blisters, plaques and urticaria. Solar urticaria: UVR-induced wheals that occurs within minutes of exposure and fades within hours. Other skin diseases exacerbated by sunlight: Several dermatologic conditions can increase in severity with exposure to UVR. These include systemic lupus erythematosus (SLE), dermatomyositis, acne, atopic dermatitis, and rosacea.Additionally, since sunburn is a type of radiation burn, it can initially hide a severe exposure to radioactivity resulting in acute radiation syndrome or other radiation-induced illnesses, especially if the exposure occurred under sunny conditions. For instance, the difference between the erythema caused by sunburn and other radiation burns is not immediately obvious. Symptoms common to heat illness and the prodromic stage of acute radiation syndrome like nausea, vomiting, fever, weakness/fatigue, dizziness or seizure can add to further diagnostic confusion. Prevention
The most effective way to prevent sunburn is to reduce the amount of UV radiation reaching the skin.
The World Health Organization, American Academy of Dermatology, and Skin Cancer Foundation recommend the following measures to prevent excessive UV exposure and skin cancer:
Limiting sun exposure between the hours of 10 am and 4 pm, when UV rays are the strongest
Seeking shade when UV rays are most intense
Wearing sun-protective clothing including a wide brim hat, sunglasses, and tightly-woven, loose-fitting clothing
Using sunscreen
Avoiding tanning beds and artificial UV exposure

UV intensity
The strength of sunlight is published in many locations as a UV Index. Sunlight is generally strongest when the sun is close to the highest point in the sky. Due to time zones and daylight saving time, this is not necessarily at 12 noon, but often one to two hours later. Seeking shade including using umbrellas and canopies can reduce the amount of UV exposure, but does not block all UV rays. The WHO recommends following the shadow rule: "Watch your shadow – Short shadow, seek shade!" Grapes
A 2022 study found that eating 60 grapes a day can stop you getting sunburn. Scientists found people who ate three-quarters of a punnet every day for two weeks were better protected against damage to the skin from ultraviolet light. Polyphenols found naturally in the fruits are thought to be responsible for the resistance. Sunscreen
Commercial preparations are available that block UV light, known as sunscreens or sunblocks. They have a sun protection factor (SPF) rating, based on the sunblocks ability to suppress sunburn: The higher the SPF rating, the lower the amount of direct DNA damage.