The flares are caused when your immune system falters. This can be due to a number of reasons. Anything from daily stressors, lack of sleep, poor nutrition, weight gain, concurrent illnesses etc may cause your immune system to be distracted from the Herpes Simplex Virus (HSV) infection. The moment that happens, the virus will flare resulting in rashes, cold sores, ulcers or blisters on your body.
Herpes simplex type 1, which is transmitted through oral secretions or sores on the skin, can be spread through kissing or sharing objects such as toothbrushes or eating utensils. In general, a person can only get herpes type 2 infection during sexual contact with someone who has a genital HSV-2 infection. It is important to know that both HSV-1 and HSV-2 can be spread even if sores are not present.