Bismuth Crystals are safe for human use, but there are a few potential side effects to be aware of. Ingesting large amounts of bismuth can lead to gastrointestinal upset. Constipation, and even kidney damage, too. Also, exposure to bismuth dust can cause irritation to the eyes, skin, and respiratory system. Some people may also experience an allergic reaction to bismuth. If you have any concerns about the potential side effects of bismuth, it’s always best to consult with a healthcare professional.