I always sunburn my head where I part my hair without one - and it's no fun at all. Exertion Higher altitudes have less oxygen. People who live at higher altitudes for a while actually have more red blood cells so they can process more air. If you are coming from a low altitude you may find that you become exhausted very quickly. Make an effort not to over exert yourself and be patient.
Most people acclimate quite quickly.
There are many plants that can only be found at higher elevations. I have noticed that poison oak seems to be a bit more virulent at higher elevations - so avoid it even if you think you are immune. I thought I was immune to poison oak until I worked south of Big Sur for a summer. Here I encountered the most powerful poison oak I have ever seen.