In order to increase your maximum health you will need silphium resin, but you must bear in mind that it can be found in two forms, the small ones, which fill a space to increase its maximum health or integrity, and the large ones that fill two spaces.
To obtain the health increase it will be necessary to fill three spaces.
Another way would be using two resins and a specific artifact,
You could also use Manufacturers, but we recommend saving enough for this.
You will be able to access your progress towards the maximum health increase from the side of the health bar.
That's all you have to know about how to increase max health by Returnal, so now that you have it, we hope you can get your health boost when you need it.