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Cold sores, sometimes called “fever blisters,” are inflamed open sores that form around the mouth. These sores are almost always caused by the herpes simplex virus (HSV).

There’s no cure for HSV, though research is making progress on a potential future cure or vaccine.

Once a person has had one cold sore, stress, sunlight, or hormonal changes can trigger the virus to activate again.

There are over-the-counter and prescription remedies that claim to treat the pain and inflammation that cold sores cause. But researchers are beginning to find that the organic compounds found in some essential oils could treat cold sores as well.

Some strains of herpes have developed resistance to the drugs used to treat them, but essential oils could potentially be effective against these strains.

The evidence that essential oils could have a significant effect on cold sores is limited and still being researched. Use them with caution and keep your doctor informed if you choose to try one out.

The Food and Drug Administration (FDA) doesn’t monitor the production of essential oils. Do some research on the brands and their quality, purity, and safety.

1. Tea tree oil

Tea tree oil has antiviral, antiseptic, and anti-inflammatory properties that can come in handy when you need to treat a cold sore.

One 2009 study found tea tree oil had a potentially antiviral effect on HSV. However, it was an in vitro study, meaning it was done on isolated samples, and it wasn’t determined if the oil was potent enough to prove very effective.

You can apply diluted tea tree oil directly to your cold sore using a clean cotton swab, but make sure you dilute it with a gentler carrier oil so you don’t hurt your skin.

Don’t use tea tree oil more than twice per day, or your skin may become irritated.

Shop for tea tree oil online.

2. Peppermint oil

Peppermint oil is another essential oil with antiseptic properties.

Peppermint oil was also included in the in vitro study for tea tree oil with similar results.

An older lab study from 2003 on HSV demonstrated that peppermint oil had the potential to calm the symptoms of an activated herpes strain — even if the strain is resistant to other kinds of drugs.

Apply diluted peppermint oil directly to the cold sore at the first sign to see if it helps symptoms.

Shop for peppermint oil online.

3. Anise oil

Oil from the anise plant has been shown in an older study from 2008 to help inhibit cold sores.

A bovine study found that anise oil could inhibit growth and development of the virus. Another in vitro study showed antiviral properties, potentially from β-caryophyllene, a chemical present in many essential oils.

Shop for anise oil online.

4. Oregano oil

Oregano oil is one of the most popular home remedies for cold sores, and for good reason. Back in 1996, oregano oil’s effects on HSV was found to be substantial.

A more recent study showed similar antiviral properties in oregano oil, potentially due to its high amounts of carvacrol, a compound found in many aromatic plants.

Rubbing diluted oregano oil on the site of your cold sore with a sterile piece of cotton may help diminish the size and inflammation of your cold sore.

Shop for oregano oil online.

5. Lemon balm oil

Lemon balm oil has been determined to inhibit herpes viruses’ penetration of cells by 96 percent for drug-resistant strains, according to a 2014 lab study. Further research is examining how lemon balm works on the herpes cells.

Since lemon balm oil can penetrate the skin layer and treat the herpes virus directly, you can apply the diluted oil directly to your cold sore up to four times per day.

Shop for lemon balm oil online.

6. Thyme oil

Thyme oil is a potent agent. It has antiviral effects on HSV, according to a lab study. Of course, if the trigger of the virus is still present — be it stress, a fever, or extended sun exposure — the virus could reactivate even after treatment.

Shop for thyme oil online.

7. Ginger oil

Ginger oil’s components have been found to reduce cold sore symptoms in a 2014 lab study.

Ginger oil feels warm on your skin and may soothe the irritation from your cold sore. Applying the diluted mixture topically may help your cold sore heal.

Consider mixing ginger oil with some of the other oils on this list in a carrier oil.

Shop for ginger oil online.

8. Chamomile oil

One study found chamomile oil to be a potential antiviral agent against HSV. It also proved potentially effective in helping to treat drug-resistant strains.

Chamomile oil also soothes the skin when applied. Applying diluted chamomile oil directly to a cold sore as soon as you feel the sore forming is the most effective way to use it.

Shop for chamomile oil online.

9. Sandalwood oil

Sandalwood oil is known for its distinct and powerful scent, but its components may also fight the cold sore virus, according to a lab study.

You can apply diluted sandalwood oil directly to a cold sore when it appears. The strong scent of sandalwood might be irritating to your nose or sensitizing to your skin, so mix it with one of the other oils on this list, as well as a carrier oil, if you choose to use this remedy.

Shop for sandalwood oil online.

10. Eucalyptus oil

Cell structure tests done in a lab revealed that eucalyptus oil might be able to reduce the duration and severity of cold sores.

Always dilute eucalyptus oil well before applying, and limit it to four applications per day.

Shop for eucalyptus oil online.

When using essential oils as a topical skin treatment, there are several things you should keep in mind.

Diluting the oils that you use for treatment with a nonabrasive carrier oil, such as coconut oil or jojoba oil, will help keep your skin from becoming further inflamed by the cold sore.

Overuse of essential oils on your skin can weaken your skin’s epidermis (outer layer) and make it harder for your skin to repair itself.

Make sure that you don’t have an allergy or sensitivity to the ingredients of your oils before using them. Do a spot test with any essential oil on another part of your skin before you apply it to an open cold sore.

Possible side effects from using essential oils to treat a cold sore range from a moderate stinging sensation to burning or bleeding at the site of the sore. Stop using the oil treatment if at any time you feel like your skin is having a negative reaction.

Remember that the claims that essential oils make aren’t necessarily evaluated by the FDA.

If you have persistent cold sores that don’t go away with treatment, you may need to speak with your doctor about preventative treatment methods.