There are plenty of obvious dangers associated with rock climbing. Along with the whole falling off and squishing on the floor thing, risks include confusing a blind hand-hold and a scorpion, and looking a bit like Tom Cruise in whichever Mission Impossible film he pisses about on a cliff face in.
However, a very real and but rarely known risk is that off permanent brain damage, or so a study in the American Journal of Medicine suggests. When high altitude climbers don't take supplementary oxygen with them, their brain tends to get a little squirly when the reach the summit.
This is caused by Hypoxia - a lack of oxygen to the brain. Most experienced climbers will know they should slowly get acclimatised to the new, high altitude conditions, and the symptoms of what is commonly called Acute Mountain Sickness will soon pass.
However, the study - conducted on 35 climbers who'd regularly complete ascents over 4000 metres, found that MRI scans on their brains showed patches of lasting brain damage - a worrying hangover from the periods of reduced oxygen.
That said,of course, if you take oxygen with you, and apply all the standard safety precautions, climbing is not just safe, but monumentally good for you. It strengthens your heart, grows muscle, thickens bones, and gives you access to views that most mortals can only dream of.