The downside is that bismuth oxycloride tends to enter the skin pores and block these pores. This would cause skin irritation. That is why some women who use mineral makeup complains that they end up with itchy and blotchy red face. Since this mineral is similar to crystals it can be itchy whenever applied.
Carmine, which is also a mineral used in mineral based cosmetics, can also cause allergies. If you have sensitive skin and you noticed that carmine is a part of the ingredient list, then it would be better to consider another product. Carmine came from the shells of cochineal beetles. The shells are crushed and there would be red pigment. This red pigment is used to provide color in cosmetics.
When exposed to allergens, the skin breaks down. The outside skin gets injured resulting to allergic symptoms like itchy patch of skin, scaly skin, or sometimes even bumps on the skin. There are studies showing that there are 10 percent of the population showing allergic reactions to cosmetics. Allergic reaction to cosmetics often occurs in women, most likely because women use cosmetic products than men.
Once you have noticed that you have an allergic reaction, stop using all the mineral makeup that you have. Then after the allergy has subsided, try using them one by one. By doing this, you would identify which of your makeup is triggering the reaction. If the symptoms would not go away even if you have stopped using the product, then it would be for the best to consult a dermatologist or your doctor.