Lucemill Menthol Crystals - 100% Natural, Soothing & Refreshing - Cold Flu Symptoms. Menthol crystals are a compound obtained from peppermint oil. They are clear to white with a cool minty fresh odour. Refreshing and cooling effect on skin, strong scent of peppermint. Simply add a few crystals of pure menthol to a bowl of hot water. Place a towel over your head in order to trap the steam. Inhale the menthol for at least ten minutes, taking care not to inhale too deeply. You will experience the soothing effects within a few minutes and notice you are able to breath a lot easier, as the steam helps soothe irritated tissue and thin blocked mucus throughout your sinuses. Ensure you do not topically apply the menthol mixture near your nostrils, as the strong menthol will cause further irritability to the already inflamed lining of the nasal passage.