An alginate is a dressing made from seaweed. In this seaweed-based dressing, calcium ions are swapped for sodium ions, which turns the dressing into a gel.
What it does well: alginate is highly porous, and the calcium ions have hemostatic properties — meaning they help stop bleeding. It is used for moderate to heavy exudative wounds, meaning wounds producing a lot of fluid, with changes every one to three days.
There is one thing about alginates worth knowing before you see it, because it alarms people who don’t expect it. The dressing may change to a yellow or brown color, which can be mistaken for purulence — that is, mistaken for pus.
That is a dressing changing color as it does its job, not a wound producing pus. The two can look similar. If you are unsure which you are looking at, that is a reasonable thing to ask about rather than to judge alone. The signs that actually point to infection are covered in the Wound Wizard pages on that subject.
The other drawbacks are simple: the dressing may stick to the wound bed when dried, it has an unpleasant odor, and it needs a second dressing over the top to keep it from drying out.
Alginates are not for minimally exudative wounds — wounds that are not producing much fluid.
Whether any of this describes your wound is not something this page can tell you. The choice of dressing, and the schedule for changing it, belongs with the clinician treating the wound.