Antioxidant density and immune signaling
Chaga (Inonotus obliquus) is a fungus that grows on birch trees. Its dark mass is rich in melanin and it contains triterpenes such as inotodiol and betulinic acid derived from the birch host, plus beta-glucan polysaccharides. In laboratory assays chaga extracts show high antioxidant capacity, and the beta-glucans are the basis for proposed immunomodulating effects, meaning they may influence immune cell activity rather than simply boosting it.
Much of the antioxidant and immune data comes from test-tube and animal studies rather than robust human trials.
Important safety caveats
Chaga is high in oxalates, and case reports describe kidney damage (oxalate nephropathy) after heavy, prolonged use, so it is not a benign tonic at high doses. It may also affect blood sugar and interact with anticoagulant and diabetes medications.
This is general educational information, not medical advice. Human evidence for health benefits is limited, the risks are real for some people, and anyone with kidney disease, on blood thinners, or managing diabetes should consult a clinician before using chaga.