Lemon eucalyptus is an effective natural oil to use as a mosquito repellent, with sharp-scented compounds proven to drive mosquitoes away. It can also make a great cleaner! Combine 1/2 cup water and 1/2 cup witch hazel (you can add a little vinegar, too) and then add 30 to 40 drops of the lemon eucalyptus oil. You can add a little more of the oil if this amount doesn’t seem to be effective.
Note: This is a potent repellent and is not child or pet friendly.
Small bugs usually hate citrus, so citrus oil sprays are common in homemade repellents. Mix equal parts water with witch hazel (a half cup of each works well). Witch hazel is an alcohol-based astringent that is commonly used in DIY repellents. (Some repellent recipes call for straight alcohol, such as vodka, but you can substitute with witch hazel, which tends to be gentler to skin.)
Add in a couple dozen drops of citronella oil, and pour it into a spray bottle. Lemon additives may also help. Remember to shake the bottle before using, and don’t spray it near your eyes.