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Why do white spots appear after extended periods in the sun?

I've noticed that my teenage sun, after he's been in the sun for a long time, seems to develop a sort of 'rash' of plain, white spots. They fade in time, but I don't understand this reaction. Does it mean he's not adequately covering up or using enough sunblock?
White spots on the skin can be due to various reasons. Have you noticed the white spots or any areas where the color of his skin is lighter or white when he has not been exposed to the sun? White spots on the skin can be due various things such as due to autoimmune causes or infectious causes. One common cause of white spots is tinea versicolor, a fungus on the skin that the body for unknown reasons cannot fight off. The fungus produces a substance that causes the skin to have lighter spots. When one goes out in the sun and gets a tan, the "normal skin" gets darker, and the affected skin looks lighter or more white in comparison. Tinea versicolor is not dangerous and it is not contagious and it typically presents in the summer, hot and humid months and can sometimes fade and re-appear. Another condition of the skin is vitiligo, a condition where the body attacks the pigment producing cells of the skin and causes white spots to appear. Again, when the non-affected skin gets darker, the affected area of the skin looks lighter or more white in comparison. Vitiligo is also not dangerous or contagious, however it can sometimes be associated with other medical conditions, so it is important to be seen by both a dermatologist and your primary care physician for further evaluation, diagnosis and treatment. As always, it is important to use sunblock when out in the sun and if spending many hours in the sun, it is important to remember to re-apply sunblock every few hours.
This answer is for general informational purposes only and is not a substitute for professional medical advice.
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