For you, going outside might mean a sunburn if you're out there too long without enough sunscreen, but for some people, any sun exposure can lead to hives and rashes within minutes!

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Sources:
https://www.merckmanuals.com/home/skin-disorders/sunlight-and-skin-damage/photosensitivity-reactions
https://www.merckmanuals.com/professional/dermatologic-disorders/reactions-to-sunlight/photosensitivity
http://www.mayoclinic.org/diseases-conditions/sun-allergy/basics/definition/con-20035077
https://www.sciencealert.com/here-s-what-happens-if-you-develop-an-allergy-to-sunlight
http://onlinelibrary.wiley.com/doi/10.1111/bjd.13930/full
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4568130/
https://www.researchgate.net/publication/284913638_Solar_urticaria
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC154188/
http://jamanetwork.com/journals/jamadermatology/fullarticle/479499
https://www.researchgate.net/profile/Marcus_Maurer/publication/225086269_Physical_Urticaria/links/09e415072b89fde8d8000000/Physical-Urticaria.pdf
http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2133.2000.03238.x/abstract
http://www.dermnetnz.org/topics/polymorphic-light-eruption/

Images:
https://commons.wikimedia.org/wiki/File:EMminor2010.JPG
https://commons.wikimedia.org/wiki/File:Misc_pollen.jpg
https://commons.wikimedia.org/wiki/File:Histamine_3D_ball.png
https://commons.wikimedia.org/wiki/File:Poison_Ivy_in_Perrot_State_Park.jpg