I've read that anti-fungal creams can be effective for cracked corners of the mouth. Sometimes a localized yeast infection is to blame.
If applying stuff and following other suggestions don't seem to help, then you might consider taking a B-complex vitamin supplement or eating more food with B vitamins- various B vitamin deficiencies include symptoms of cracked lips and cracked mouth corners. Read some of these links.
If applying stuff and following other suggestions don't seem to help, then you might consider taking a B-complex vitamin supplement or eating more food with B vitamins- various B vitamin deficiencies include symptoms of cracked lips and cracked mouth corners. Read some of these links.