Whats the white milky stuff thats coming from my red onion?!

Whats the white milky stuff thats coming from my red onion?

I just cut my red onion and this white milky stuff that is super strong and smells like onion dripped from it. Does this mean it is no good?

Thanks.

I've had that happen to my onions, and I always toss them. Maybe it is just the "sugar" coming from the onion (WTF?), but why risk it? It's probably old and becoming rotten.