Propylene glycol is used as an antifreeze in cars and trucks.
If you want to use essential oils, however, you'll have better luck combining 1 ounce essential oil, 2 1/4 ounces pre-formulated reed diffuser oil base or fragrance grade dipropylene glycol, and 1/4 ounce perfumer's alcohol.
Steer clear of anything that contains propylene glycol, sodium lauryl sulfate, sodium laureth sulfate or parabens, just to name a few of the ingredients that are often debated in the industry.
In addition to being aluminum free, it is also free of parabens, propylene glycol and harsh chemicals, all of which may contribute to skin irritation.
Some questionable ingredients, like propylene glycol and sodium sulfate, are found in fading cleansers and may irritate the skin.