Rosemary essential oil may be used in bath rituals, but it should first be mixed with a suitable dispersing base. Essential oils do not dissolve properly in plain water; if drops are added directly to a bath, they can remain concentrated on the surface and come into contact with the skin in uneven patches.
A dispersing base helps the essential oil spread more evenly in the bath. Follow the instructions for the base product you are using, and keep the amount modest because rosemary oil has a strong, herbal, camphor-like aroma. If you are new to this scent, start cautiously rather than making the bath heavily scented.
Rosemary oil is often chosen for a more stimulating, fresh aromatic experience, so it may not be the best choice when you want a very soft or sleep-oriented bath scent. Avoid contact with the eyes and mucous membranes, and do not use essential oils in a bath if your skin is irritated or unusually sensitive. If you are pregnant, breastfeeding, have very sensitive skin, or are preparing a bath for a child, check suitability before use.