Essential Oil Blends by DoTerra. Details:doTERRA On Guard, a proprietary essential oil blend, provides a natural and effective alternative for immune support. As one of doTERRA’s best-selling blends, doTERRA On Guard protects against environmental and seasonal threats with essential oils known for their positive effects on the immune system. doTERRA On Guard can be taken internally on a daily basis to maintain healthy immune function and support healthy cardiovascular function. It can also be used on surfaces throughout the home as a non-toxic cleaner. When diffused, doTERRA On Guard helps purify the air and can be very energizing and uplifting. Add two to three drops in a veggie capsule for an immune boost. Add to water for an effective all-purpose surface cleaner. Soak sliced apples in water and a few drops for a healthy, immune-boosting snack. Combine a few drops of doTERRA On Guard with Fractionated Coconut Oil for a natural hand cleanser.