Cold sores are a very common illness caused by the herpes simplex virus (HSV).

The disorder is characterized by groups of fluid-filled blisters, which appear on red swollen areas of the skin or on the mucous membranes. The areas can be tender and painful. The blisters heal without scarring but have a tendency to recur.

Cold sores — also called fever blisters — are quite different from canker sores, a condition people sometimes associate them with. The herpes simplex virus causes cold sores, and they're contagious. Canker sores, which aren't contagious, are ulcers that occur in the soft tissues inside your mouth, places where cold sores don't occur.

Cold sores are caused by a viral infection that attacks the skin and nervous system. Cold sores are small, painful, fluid-filled blisters on the mouth or nose.

The cold sore virus is typically transferred through direct or indirect physical contact. Examples of direct contact include viral transmission during kissing or other intimate behaviors. Indirect contact can occur when live virus is transferred between children putting commonly shared objects into their mouths, use of someone else’s face cloth, drinking from a common cup or glass and sharing of cosmetics, such a lipstick.

Often, transmission is between family members due to normal contact. A kiss from a friend or relative when he or she has a lesion can introduce the virus to a person who may not have been previously exposed.

Cold sores usually appear on your lips. Occasionally, they occur on your nostrils, chin or fingers. And, although it's unusual, they may occur inside your mouth — but only on your gums or hard palate, which is the roof of your mouth. If the sore appears on other soft tissues inside your mouth, it may be a canker sore, but it's not a cold sore.

Prior to a clinical outbreak of a recurrent cold sore episode, many people experience a prodromal phase, which includes an itchy, tingling sensation on the soon-to-be-affected skin. Often there is a warm or burning sensation with tenderness to touch soon thereafter. As the disease progresses, the area becomes red and raised. Tiny fluid filled bumps called vesicles form and join together.

After a 3- to 7-day incubation period, fluid-filled vesicles appear, usually on the cervix (the primary infection site) and possibly on the labia, perianal skin, vulva, or vagina of the female and on the glans penis, foreskin, or penile shaft of the male. Extragenital lesions may appear on the mouth or anus. In both males and females, the vesicles, usually painless at first, will rupture and develop into extensive, shallow, painful ulcers, with redness, marked edema, tender inguinal lymph nodes, and the characteristic yellow, oozing centers.

People who have areas of broken skin (like eczema), or people who have other serious illnesses, must be careful during their first infection as it can spread over all the area of broken skin. Rarely, people develop erythema multiforme following each cold sore; they may be given antiviral tablets.

Occasionally, when a person first catches it, he/she gets ulcers inside the mouth and throat as well as, or instead of, the usual sores on the lip. There could be a fever and other flu-like symptoms. A painkiller can help: aspirin, ibuprofen or paracetamol - always follow the instructions on the packet.

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