1 You can transmit the viruses at this time even though sores aren't yet visible. 2  Not everyone who gets cold sores will notice symptoms during the prodromal period. 3  Small, painful blisters appear. 4  They break and ooze a clear fluid, form a painful sore, and then form a crust or a scab. 5  Cold sores usually heal on their own.
http://www.healthyhorns.utexas.edu/ht_coldsores.html
Causes. Cold sores are caused by certain strains of the herpes simplex virus (HSV). HSV-1 usually causes cold sores. HSV-2 is usually responsible for genital herpes. However, either type can cause sores in the facial area or on the genitals. Most people who are infected with the virus that causes cold sores never develop signs and symptoms. Cold sores are most contagious when oozing blisters are present. But you can transmit the virus to others even if you don't have blisters. Shared eating utensils, razors and towels, as well as kissing, may spread HSV-1. Oral sex can spread HSV-1 to the genitals and HSV-2 to the lips. Once you've had an episode of herpes infection, the virus lies dormant in nerve cells in your skin and may emerge as another cold sore at the same place as before.
http://www.mayoclinic.org/diseases-conditions/cold-sore/basics/causes/CON-20021310
Cold sores spread from person to person by close contact, such as kissing. They're caused by a herpes simplex virus (HSV-1) closely related to the one that causes genital herpes (HSV-2).
http://www.mayoclinic.org/diseases-conditions/cold-sore/basics/definition/CON-20021310
353,164 Helpful Votes. 388 Followers. A. Cold sores and fever blisters are caused by the herpes simplex virus type 1. Unlike canker sores, cold sores and fever blisters are contagious from the time the blister ruptures to the time it has completely healed. The initial infection often occurs before adulthood and may be confused with a cold or the flu.
http://answers.webmd.com/answers/1190129/are-cold-sores-or-fever-blisters
Both of these viruses can affect your mouth or genitals and can be spread by oral sex. Cold sores are contagious even if you don't see the sores. There's no cure for HSV infection, and the blisters may return. Antiviral medications can help cold sores heal more quickly and may reduce how often they return. 1  Symptoms.
http://www.mayoclinic.org/diseases-conditions/cold-sore/basics/definition/CON-20021310
1 Not everyone who gets cold sores will notice symptoms during the prodromal period. 2  Small, painful blisters appear. 3  They break and ooze a clear fluid, form a painful sore, and then form a crust or a scab. 4  Cold sores usually heal on their own.
http://www.healthyhorns.utexas.edu/ht_coldsores.html
Introduction. Cold sores are small blisters that develop on the lips or around the mouth. They are caused by the herpes simplex virus and usually clear up without treatment within 7 to 10 days. You will not have any symptoms when you first become infected with the herpes simplex virus.
http://www.nhs.uk/Conditions/Cold-sore/Pages/Introduction.aspx
1 About 6 to 48 hours before a cold sore appears, you may feel itching, tingling, burning and/or pain at the outbreak site. 2  You may run a low fever (less than 100.5 degrees F or 38 degrees C). 3  This is called the prodromal period.
http://www.healthyhorns.utexas.edu/ht_coldsores.html
The strain of herpes simplex virus usually responsible for cold sores is known as HSV-1. In rare cases, cold sores can also be caused by the herpes simplex virus type 2 (HSV-2). This can be the result of having oral sex with someone who has genital herpes. Read more about the causes of cold sores.
http://www.nhs.uk/Conditions/Cold-sore/Pages/Introduction.aspx
Cold sores — also called fever blisters — are a common viral infection. They are tiny, fluid-filled blisters on and around your lips. These blisters are often grouped together in patches. After the blisters break, a crust forms over the resulting sore. Cold sores usually heal in two to four weeks without leaving a scar.
http://www.mayoclinic.org/diseases-conditions/cold-sore/basics/definition/CON-20021310
how long are cold sores contagious
Cold sores are contagious from the time the blister ruptures to the time it has completely healed.