The first episode may be mild or severe. It usually occurs in children between 1 and 5 years old.

• First symptoms usually appear within 1 or 2 weeks, and as long as 3 weeks, after contact with the virus. Sore throat and fever that can last up to 5 days may occur before the blisters appear. There may also be swollen glands in the neck.
• First episode may last 2 to 3 weeks. The lesions may be on the gums, in the mouth and throat, or on the face. It may hurt to swallow.

Later episodes are usually milder.

• May be triggered by menstruation, sun exposure, fever, stress, or various other unknown causes.
• Warning symptoms of itching, burning, increased sensitivity, or tingling sensation may occur about 2 days before lesions appear.

An outbreak usually involves:

• Skin lesions or rash around the lips, mouth, and gums
• Small blisters (vesicles) filled with clear yellowish fluid
  • Blisters on a raised, red, painful skin area
  • Blisters that form, break, and ooze
  • Yellow crusts that slough to reveal pink, healing skin
  • Several smaller blisters that merge to form a larger blister

Diagnosis is made on the basis of the appearance or culture of the lesion. Examination may also show enlargement of lymph nodes in the neck or groin.

Viral culture, viral DNA test, or Tzanck test of the skin lesion may reveal the herpes simplex virus.