The EPA’s list of effective, safe insect repellents is a short one, for both chemical and natural methods. A special kind of eucalyptus oil makes the cut. Oil of lemon eucalyptus (OLE) has a chemical called PMD that shoos away mosquitoes and other bugs. But don’t use it on children under 3. OLE has a different chemical makeup from lemon eucalyptus oil, although their names are similar.

Research suggests that the oil fights respiratory infections by killing bacteria, viruses, and fungi. This is why you can find it in saline nasal wash. It also causes the tiny hair-like filaments in your lungs (called cilia) that sweep out mucus and debris from your airways to move faster. This can also fight infections.

Eucalyptus is a key ingredient in some topical analgesics. These are pain relievers you apply directly to your skin, such as sprays, creams, or salves. While it’s not the main painkiller, eucalyptus oil works by bringing a cold or warm sensation that takes your mind off the pain.

In one clinical trial, people who breathed in eucalyptus oil after knee replacement surgery felt less pain and had lower blood pressure. Researchers think this may be due to something in the oil called 1,8-cineole. It may make your sense of smell work with your nervous system to lower your blood pressure.

Eucalyptus oil not only can help with pain post-op, but it also may help keep you calm before surgery, too. Researchers measured the effect on anxiety of breathing in essential oils in people about to have surgery. Before their operations, they smelled different oils for 5 minutes. The 1,8-cineole in eucalyptus oil worked so well that researchers suggested it may be useful for entire procedures.

Wondering if herbal toothpaste works as well as the standard stuff? Possibly. One small study compared a natural toothpaste containing eucalyptus with a standard toothpaste. Researchers tested both kinds on 30 people with gingivitis (a common, mild gum disease that causes swelling and redness) and plaque buildup (the sticky film that coats your teeth when you don’t brush enough). Both toothpastes worked equally well to lessen these problems.

Brushing isn’t the only way to tap the power of eucalyptus oil for a healthy smile. Chewing gum that has it as an ingredient can take down dental culprits like plaque, gingivitis, and bleeding, too. Some dentists say chewing sugar-free gum is good for stimulating your salivary glands and keeping your mouth moist. Just remember, it’s not a replacement for brushing and flossing.

Eucalyptus can do more than look pretty and smell divine. The oil is handy around the house, too. It’s the active ingredient in more than 30 cleaning products approved by the EWG, a nonprofit environmental research group. In one study, it removed bacteria including E.coli from steel surfaces.

Take this, lice. A treatment of eucalyptus and tea tree oil did twice as well in a clinical trial as the old standby, pyrethrin. Not only did it kill 100% of lice and eggs, but it did it in only one dose. Other treatments needed several. Tests on skin revealed no irritation for adults or children, too.

Are rats scurrying just a little too close for comfort? Keep them away with a eucalyptus oil solution. Spray it regularly in places where you see them. Many of the chemicals in it -- especially 1,8-cineole -- deal a powerful punch to pests. It’s kinder to the environment than harsh chemicals, too.

Eucalyptus oil shows promise as a defense against HSV-1, or oral herpes. In one lab study, it outperformed the standard herpes medication, acyclovir. The 1,8-cineole chemical in the oil shuts down virus particles and may block them from entering cells. In lab tests, eucalyptus oil was able to curb the spread of the virus by more than 96%.

Though eucalyptus oil has many benefits, the undiluted form can be highly toxic if you take it by mouth. Just 2-3 milliliters can trigger dizziness, drowsiness, and loss of muscle control. Five milliliters or more can lead to nervous system shutdown and even coma. Symptoms show up between 30 minutes to 4 hours after exposure. A small number of people have had epileptic-like seizures within a few minutes of inhaling eucalyptus oil.