Rose in greenhouses, and in warmer countries they may also be grown under cover in order to ensure that the flowers are not damaged by weather and that pest and disease control can be carried out effectively. Significant quantities are grown in some tropical countries, and these are shipped by air to markets across the world. Some kind of roses are artificially coloured using dyed water, like rainbow roses. Rose perfumes are made from rose oil (also called attar of roses), which is a mixture of volatile essential oils obtained by steam distilling the crushed petals of roses. An associated product
Lavandula oil, and its major constituent linalyl acetate, are toxic to human skin cells "in vitro," contact dermatitis to lavender oil appears to occur at only a very low frequency." There are two reports on a total of six cases of gynecomastia in prepubertal boys who were exposed to topical lavender essential oil. A 2007 study examined the relationship between various fragrances and photosensitivity, stating that lavender is known "to elicit cutaneous photo-toxic reactions", but does not induce photohaemolysis. Flower spikes are used for dried flower arrangements. The fragrant, pale purple flowers and flower buds are used in potpourris. Lavender is