Rosemary essential oil is used externally to treat a variety of conditions including rheumatism and as a tonic for a dry, scaly scalp. However, using this oil during pregnancy is a bad idea, says Shirley Price, author of “Aromatherapy for Common Ailments.” In fact, you should not use any type of essential oil without first checking with your doctor.
Rosemary is a uterine stimulant in very high doses. Avoid the oil entirely during pregnancy, as it can cause miscarriage.
Rosemary is included on the list of diuretic and emmenagogic oils, meaning it can induce menstruation and may deplete fluid in the fetal sac. Other oils on this list include juniper berry, marjoram, sweet fennel and clary sage.
Rosemary oil’s negative effects in pregnancy are mainly attributed to its camphor content, according to “The Essential Guide to Herbal Safety,” by Simon Mills and Kerry Bone. However, studies on camphor have not always backed this theory up, Mills and Bone note. The main constituents in rosemary oil are p-cymene, linalool, gamma-terpinene, beta-pinene, alpha-pinene, eucalyptol and thymol.
Rosemary oil is for external use only because ingesting it can be toxic. Putting it on your skin can cause internal effects--such as miscarriage--because your skin is somewhat permeable. That means its active chemicals are absorbed via your skin, just like ingredients in pharmaceuticals like nicotine patches.
While rosemary oil is considered unsafe if you are pregnant, consuming the herb in culinary dishes is safe, despite the fact that rosemary leaves contain the volatile oil. Rosemary, as opposed to the essential oil, is in pregnancy category B1, meaning it does not increase the frequency of fetal malformation or other problems with limited use or it has not shown evidence of increased frequency for fetal damage in animal studies. Ingesting the herb in large amounts is not recommended for anyone, however, because it can cause spasms, vomiting, coma and fluid in the lungs, say the experts at the University of Maryland Medical Center.