There are 3 ways that players can regain lost health, but the most efficient way to heal is through

BLOOD BAGS
The Blood bags is the easiest way to heal in the game , these Blood Bags can be made or crafted in safe rooms using 10 resins and 15 Chiral Crystals . They can be also found in and around the boss fight locations . The item can be found in the inventory after being picked up in the boss fights locations or crafted . Thus by just using the item you can heal instantly .

CRYPTOBIOTES
A Cryptobiote is a small creature found in the wild , when ingested, replenishes a small amount of a person’s blood. These creatures are pretty rare and can mostly be found in coral formations. They can also be picked up and stored in the inventory

PRIVATE ROOMS
Resting in private rooms is the last method one can use to heal themselves in Death Stranding 2 . By Resting in private rooms one can replenish the health and stamina completely . This method is much more efficient compared to the other methods