Any hand sanitizer formulas should contain no more than 1% of essential oil. That means, 1 drop of essential oil in every 5ml of base (5ml = 100 drops). So if you are making 100ml of your hand sanitizer, add no more than 20 drops of essential oil. Essential oils are potent chemical compounds and can be damaging when use in excess or in high concentration. And do not use undiluted or internally. When in doubt, please seek professional advice.