To treat cold sores at home, it is important to begin treatments at the first sign of a cold sore. You may not be able to prevent them, but early treatment can drastically reduce the severity of a cold sore. Lysine supplements can help to reduce cold sores. Avoid touching them, sharing cups or utensils, or kissing another person, to avoid spreading the virus. Often, cold sores appear with other illnesses, so treat those, too.