Basic chemistry, many studies, and decades of use have shown that benzoyl peroxide is safe and effective. However, there are a few things about which you may want to be aware.
Allergy: While allergy to benzoyl peroxide is rare, is does sometimes occur. To test for allergy, apply a nickel size amount of benzoyl peroxide to your inner forearm for 2-3 nights. If you experience swelling and/or severe crusting, do not use benzoyl peroxide. If your skin fares well, test on your temple for another 2-3 nights. Again, if you see swelling and/or severe crusting, discontinue use of benzoyl peroxide. If you are unsure or have any doubt, check with your doctor.
Less than 1:1000 people experience contact sensitization to benzoyl peroxide over time. Symptoms can be confused as a worsening of the disease but are in fact due to contact sensitization.
Benzoyl peroxide has not been studied in pregnant mothers. Consult your physician before using any medication, topical or otherwise, during pregnancy.