Health upgrade reinforces the mining suit in order to sustain more damage during the ever-increasing danger of mining runs. It's not essential at the beginning, since there aren't any real threats to reach 0 health, but at some point is a good idea to start upgrading it.
Reinforce your suit to sustain more damage in the mines.
Equipped at start
Buffed up your weakspots to sustain more damage in the mines.
Beef up your suit to take more hits out in the mines.
Toughen up your exterior and take more damage when exploring.
Bulk up your suit and take a bullrat charge head-on!
Take a slug explosion head-on with an improved suit!
Build up your suit's defensive capablities and survive deeper depths.
Protect your suit with a thin, invisible barrier and defend against major damage.
Become ironclad and take more damage from hostile enemies.
You're like a walking tank, uh, more or less. Travel the deepest depths with minimum worry.
Health is at the current Maximum