The common cause of blisters on the lips is herpes simplex virus infection, which is self-limiting and will recover on its own, even if left untreated. If it does not improve in the long run, the recovery process can be speeded up by applying acyclovir ointment and penciclovir cream to the lesions on the advice of your doctor. But the main way is to live a regular life, eat a healthy diet and keep your body in good shape.