Neem, clove, citronella, and lemon eucalyptus oils are extremely effective. You can choose any one of these as the primary oil and if you add in another from this group, it will have enhanced synergistic effectiveness. Essential oils can burn or irritate the skin if applied directly alone. So we need to dilute with a skin-safe oil. Coconut oil is a wonderful carrier oil because it is soothing and healing, and will dilute and calm irritating factors of the essential oils. Thus, the coconut oil allows us to use a percentage of essential oil which makes a strong and long-lasting repellent.

The following is one example of a recipe which has very high effectiveness:
2 drops of neem oil + 3 drops of lemon eucalyptus oil + 1 teaspoon organic extra virgin coconut oil

OR TO MAKE A LARGER AMOUNT of REPELLENT: 60 drops (1/2 tsp) TOTAL of essential oils + ¼ cup (60 ml) coconut oil

You can use 12 drops of essential oil and 1 teaspoon of coconut oil to make a higher concentration which might work better if mosquitos are especially thick.
Rub a very small amount of the repellent onto the skin (keep out of the eyes). Reapply after swimming or bathing or excessive perspiration. Store leftover repellent in a dark bottle out of sunlight and away from heat.

IMPORTANT SAFETY NOTE: Some people are very sensitive to essential oils. I would recommend testing the repellent you make by rubbing a small amount on the inside of a wrist and sleeping with it on overnight. If any redness develops, do not use that essential oil in the repellent and test another oil mixture on the other wrist the next night.

(From the July/August 2014 issue of The Well Being Journal)

Homemade Insect Repellent as Effective as DEET