Can I kiss with a cold sore, and when can I kiss again?

How long is a cold sore contagious?

Cold sores are caused by the herpes simplex virus, most often HSV-1. The NHS says they are contagious from the moment you first feel tingling or other early signs, and that they stay contagious while they heal. They usually clear up on their own within 10 days.

Cold sores tend to move through stages: tingling or itching, then blisters, then the blisters burst and crust over into a scab, then the scab falls off. Every one of those stages counts as contagious. A scab is not the finish line.

• Tingle or itch: contagious, no kissing
• Blisters: most contagious, no kissing
• Scab: still healing and still contagious, no kissing
• Scab gone, normal skin: the usual point most people start kissing again

Who should I never kiss with a cold sore?

Some people can get very sick from the cold sore virus. The NHS warns that kissing a baby while you have a cold sore can lead to neonatal herpes, which is very dangerous to newborns. The American Academy of Pediatrics says the virus is dangerous to babies under 6 months old, especially in the first few months of life.

MedlinePlus says herpes infection can be severe in people with a weakened immune system, and widespread infection can be life threatening. That includes people having chemotherapy, organ transplant patients and others on medicines that weaken the immune system. The NHS also flags pregnant people as a group that may need hospital advice.

• Newborns and babies under 6 months, including a quick kiss on the head or hands
• Anyone with a weakened immune system
• Pregnant partners, especially near the due date: ask their doctor or midwife
• Children with eczema: the AAP says new blisters on a child with eczema need a call to the pediatrician

Can a cold sore spread through oral sex?

Yes. The NHS says not to have oral sex until a cold sore completely heals, because you could give your partner genital herpes. The CDC says HSV-1 from the mouth can spread to the genitals through oral sex, which is why some genital herpes is caused by HSV-1.

Apply the same rule as kissing: no oral sex from the first tingle until the sore is fully healed.

What about lip balm, cups and towels?

MedlinePlus advises against sharing utensils, straws or glasses when someone has oral herpes. The American Academy of Pediatrics adds towels, toothpaste and other personal items during an outbreak. Lip balm touches the sore directly, so treat it the same way.

Wash your hands with soap and water every time you touch the sore, and avoid touching it except to dab on cream. The virus can spread to other parts of your body, including your eyes, where it can cause a serious eye infection.

• Cups, water bottles, straws and cans
• Forks and spoons
• Lip balm, lipstick and lip gloss
• Towels and face cloths
• Vapes and anything else that touches your lips

Does Valtrex or aciclovir make it safe to kiss sooner?

Not on its own. Antivirals like aciclovir, valacyclovir (Valtrex) and famciclovir can ease pain and shorten an outbreak, and they work best when started at the first tingle, before blisters form. For cold sores, valacyclovir is taken as 2 doses 12 hours apart. MedlinePlus says antiviral skin creams usually shorten an outbreak by only a few hours to a day.

None of the sources we checked say that taking an antiviral makes an active sore safe to kiss. The sore can still spread the virus until it is healed. What medicine can do is get you to the healed stage sooner. Valacyclovir also does not cure herpes, so the virus stays in your body and can cause future cold sores.

Can I spread the virus when I don't have a sore?

Yes, though the risk is lower than with an active sore. MedlinePlus says oral herpes can sometimes spread even when you do not have mouth sores or blisters, and the CDC says the skin can shed the virus from areas with no visible sore. This is called asymptomatic shedding.

That means no one can promise zero risk between outbreaks. It is still worth waiting until a sore heals, because spread is easiest during an active outbreak. If your partner has never had cold sores and you get them often, ask a clinician whether daily antiviral medicine makes sense for you.