How does helium affect your lungs

When you breathe in helium from a balloon, why does your voice turn all high and squeaky?
and does it affect your health in anyway?

Well when you speak, air bounces around your vocal cords to produce sensible sounds. Helium is a lighter gas than oxygen, so when you have helium in your lungs and you talk, it resonates through your vocal cords differently and provides a higher-pitched product. It normally doesn't affect your health in any serious ways, but keep in mind that it does displace oxygen in your lungs, so don't suck too much up or you'll pass out.

The helium is lighter than oxygen and therefore it puts less pressure on your lungs, than oxygen does normally and so the less presure on your lungs the lighter you voice.
The only health effects it has on you is the fact that if you ingest helium repeadidly instead of oxygen, than you body will obviously not have any oxygen, and you'll die (After continual helium breathing)

No helium is not poisonous but u might suffocate if you breathe a whole lot of it continuously due to lack of oxygen. Helium is a light gas and sound waves travel faster in helium compared to plain air. So your voice becomes squeaky and high pitched due to the sound travelling faster