Regardless whether the SPF begins to directly lessen, the cream itself will begin to deteriorate, eventually taking the SPF with it. However, the cream should be good for several months. If you use the product year around, purchase smaller amounts and a new container each three to six months gto be safest.
Check with your physician about using suncream while using any vitamin supplements or medications that you may be taking; sometimes there is a nasty side effect because of combinations. Alternatively, check with MedLiine online.