TIL: Generally all plastics exposed to UV start to photodegrade. If you google why old computers turn particularly yellow most sources point to bromine-based flame retardant agents in the plastic, but some people make a convincing case[1] that ABS just naturally turns yellow in UV light.

Not much real research into that topic, interestingly.

[1] https://medium.com/@pueojit/a-look-into-the-yellowing-and-de...