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No one knows for sure what causes the nausea and vomiting. Increasing levels of hormones may play a role. Hormonal changes also may heighten your sense of smell and make you much more sensitive to certain odors. These changes can cause your sense of taste to be “off”—you may have a sour or bitter taste in your mouth, or nothing may taste good to you.

See Morning Sickness: Nausea and Vomiting of Pregnancy to learn more.

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Published: October 2020

Last reviewed: October 2020

Copyright 2020 by the American College of Obstetricians and Gynecologists. Read copyright and permissions information.

This information is designed as an educational aid to patients and sets forth current information and opinions related to women’s health. It is not intended as a statement of the standard of care, nor does it comprise all proper treatments or methods of care. It is not a substitute for a treating clinician’s independent professional judgment. Read ACOG’s complete disclaimer.