Essential oils are known to cross the blood-brain barrier, so it's accepted that they also cross the placenta, according to Janetta Bensouilah and Philippa Buck, authors of "Aromadermatology." Oils with known toxicity, therefore, should be avoided throughout pregnancy. The good news? Several essential oils are considered safe during pregnancy. Julia Lawless, author of "The Encyclopedia of Essential Oils" recommends that pregnant women use only half the stated amount when indulging in these oils. Avoid taking essential oils internally.

Jasmine

Jasmine is an essential oil you can safely use during pregnancy, according to Valerie Ann Worwood, author of "The Complete Book of Essential Oils and Aromatherapy." This fragrant, amber-colored oil has a medium consistency. Its primary uses are to ease anxiety, boost mood, soothe respiratory illnesses and relieve skin conditions, including acne and eczema. Jasmine essential oil is also known as an aphrodisiac.

Lavender

Lavender, according to Worwood, is another safe essential oil for pregnant women. According to New York University Langone Medical Center, traditional use of lavender essential oil involves external application for treatment of joint pain, muscle aches and a variety of skin conditions, including acne, eczema, burns and insect stings. It's also used as a hair rinse and as a fragrance in potpourri.

Geranium

Geranium essential oil is extracted from the geranium plant. Its fragrance is floral, reminiscent of a rose. Geranium is known for its calming, balancing and uplifting effects, according to Susanne Fischer-Rizzi, author of "Complete Aromatherapy Handbook: Essential Oils for Radiant Health." Geranium oil is used topically as an antiseptic or astringent and for treating wounds and skin disorders such as shingles and eczema. As a lotion, it may be beneficial for inflamed or irritated skin. Worwood indicates that geranium is safe for pregnant women.

Chamomile

In aromatherapy, Roman chamomile is widely used as an anti-inflammatory and calming essential oil, according to Jennifer Peace Rhind, author of "Essential Oils: A Handbook for Aromatherapy Practice." Rhind notes that it's obtained from the daisy-like flowers of this creeping perennial, which was a staple of English herb gardens. Chamomile oil is known for its distinctive pale blue color and strong, fruity, apple-like fragrance. Worwood includes chamomile on her list of essential oils that are safe to use during pregnancy.