Zac Efron thinks he looks like "a zombie" after catching poison oak.

The 'High School Musical' star developed the skin condition - which is dermatitis caused by the sap of poison ivy - after going cliff jumping with friends and he has now started to resemble one of the undead.

He explained: "I went backpacking over Memorial Day weekend (at the end of May) and I just got the worst poison oak. It was my first time getting it. Dude, it's like everywhere - everywhere! I can't even begin to show you, because you'll get so grossed out. I look like a zombie from 'Dawn of the Dead'."

Zac tried to dodge the poisonous plant but felt it brush his back as he jumped off the cliff and immediately knew he had contracted the condition, which has left the hunk with itchy, inflamed and blistered skin.

The 22-year-old actor - who is dating Vanessa Hudgens - has had to "air out" awkward parts of his body, but admits any opportunity he gets to wash and soothe the pain feels like "the best orgasm ever".

Speaking about his treatment, Zac added in an interview with Details magazine: "Oh my God, it's like the best orgasm ever! I'm just airing it out. It just itches too much."