Astaxanthin is a carotenoid and belongs to the group of phytochemicals. It is responsible, for example, for the natural red coloration of the microalga Haematococcus pluvialis. And that’s not all: Astaxanthin serves as UV protection for the microalgae, which is why it produces more astaxanthin under stressful conditions, such as increased UV radiation. As a particularly powerful antioxidant, astaxanthin can also protect human cells from oxidative stress.