There are a few different reasons why sunlight can give you a headache. One reason is because of the glare. When the sun is shining directly into your eyes, it can cause a lot of strain on your eyes and lead to a headache. Another reason is because of the heat. When it’s hot outside, your body temperature rises and this can also lead to headaches. Finally, if you’re dehydrated or not getting enough water, this can also contribute to headaches. So if you find that sunlight is giving you headaches, make sure to stay hydrated and try to avoid being in direct sunlight for too long.