Skydraul is the most heinous stuff made, and horribly toxic. It causes permanent nerve damage too if you are exposed to enough of it. A major airline I previously flew for had a whole bunch of MD-80's and for some reason the APU's (small turbine engine in the tail to power aux equipment) was alledgedly sucking in misted skydraul (from a badly placed HYD pump) into the pneumatic supply when running the air conditioning at the gate to cool the aircraft. Not all aircraft, but some. It was a big flap, many flight attendants claimed severe injury over time and were convinced their symptoms would be aggrevated when flying on certain tail number MD-80's, etc. One time I was operating one of these certain known aircraft and the ladies in back were going nuts and saying they smelled skydraul. So I turned off the APU immediately and went into the tail section to investigate. It was like a bad horror film - the guy who "investigates" always gets hosed. I opened the door to the tailcone area and immediately felt misted fluid and smelled a nasty substance. Thank god I didn't breathe too deeply and had my sunglasses on just in case. The airplane was grounded for the day - the whole back end had to be cleaned up. Needless to say I washed up immediately but had one hell of a headache afterward for about an hour. Not sure if it was just a mental reaction to the flap or a seriously physical reaction to this day but it's bad stuff.