system
Given the following post, respond as if you're commenting on Reddit:
human
Why is hydraulic fluid so toxic to humans ? (questions stems from recent pics of a NSFW hand that was operated on to remove high pressure fluid from a leak)
gpt
Aircraft hydraulic fluid is phosphate-ester based. Phosphates dissolve oils very well; they were a standard component of electric dishwasher detergent until recently, when they were removed over groundwater pollution concerns. It's chosen because it's incompressible, less dense than oil (lighter), and is very temperature-stable.

Automotive brake fluid, on the other hand, is based on glycol ethers. In this case, the composition is chosen for its very high boiling point and thermal conductivity. In a passenger car the brake fluid might see a temperature of 400F; in a race car 500F+. Glycol ethers are a common solvent used in paint, and they are very hygroscopic (absorb water) which makes them a skin irritant, but their toxicity is considered low.