Sleep talking, known medically as somniloquy, is a type of parasomnia in which a person speaks, vocalizes, or makes sounds during sleep without being aware of it. It is a common and generally harmless phenomenon that can range from simple sounds, mumbling, or single words to full sentences and even animated conversations. Sleep talkers have no memory of what they said when they wake up. Sleep talking can occur during any stage of sleep. When it happens during non-REM sleep — particularly deep sleep — the content is often meaningless or garbled. Sleep talking that occurs during REM sleep, when dreaming is most active, may be more coherent and may reflect the content of the person’s dreams. Sleep talking is particularly common in children, with studies suggesting that up to 50 percent of children talk in their sleep at some point. It tends to decrease in frequency with age but can persist into adulthood. It is more common in males than females. Triggers for sleep talking include sleep deprivation, fever, stress, alcohol consumption, certain medications, and other sleep disorders such as REM sleep behavior disorder and sleepwalking. Emotional stress or anxiety during the day can also increase the likelihood of sleep talking. Sleep talking is generally harmless and does not require treatment in most cases. It is more of a nuisance to bed partners than to the person doing it. Improving overall sleep quality by addressing contributing factors such as stress and sleep deprivation may help reduce its frequency. If sleep talking is loud, frequent, or accompanied by other symptoms such as violent behavior, it may warrant evaluation by a sleep specialist.