Board Thread:The Quarters - Q & A/@comment-71.168.228.161-20140616210925/@comment-24244390-20140617012804

As you level up your constitution score increases, and you can also increase it by buying stronger armor. This decreases most sources of damage. You also gain access to skills and potions that can restore HP. Having a fixed max HP is unusual among RPGs and I don't know why the designers made that choice -- but mechanically speaking, the effects of increasing constitution are the same as increasing HP (either way, as you level up you're able to survive a greater number of damaging events).