You will want to look for 100% undiluted pure essential oils. If theyâ€™re truly undiluted, you wonâ€™t have to put your nose right up them to get a good whiff. You should be able to hold it about 5 inches away and still get a good smell. Another way to determine if theyâ€™re undiluted is by putting a drop on a piece of paper. If it leaves an oily stain on the paper, itâ€™s probably been diluted with a vegetable oil.