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Do you listen to quiet music to help you wind down before sleep? However, this practice could be counter-productive, according to a new study by Michael K. Scullin and colleagues at Baylor University. The work, published in Psychological Medicine, found that bedtime music was associated with more sleep disruptions and that instrumental music is even worse than music with lyrics.

In the first study, 199 online participants living in the US reported on their sleep quality and music listening frequency and timing, as well as their beliefs about how this affected their sleep. Almost all—87%—believed that music improves sleep, or at least does not disrupt it. However, the team found that more overall time spent listening to music was associated with poorer sleep and daytime sleepiness. Just over three quarters of the participants also reported experiencing frequent “earworms”—having a song or tune “stuck” and replaying in their minds. A quarter reported experiencing these during the night at least once per week, and these people were six times as likely to report poor sleep quality. The team’s analysis suggested that listening specifically to instrumental music near bedtime was linked to more sleep-related earworms and poorer sleep quality.

The team then ran an experimental study on 48 young adults. After arriving at the sleep lab at 8:45 p. m., participants went to a quiet bedroom, where they completed questionnaires that included measures of stress, sleep quality and daytime sleepiness. They also had electrodes applied, ready for the night-time polysomnography to record their brain wave activity, as well as heart rate and breathing, and reported on how relaxed, nervous, energetic, sleepy and stressed they felt. At 10:00 p. m., they were given some “downtime”, with quiet music playing. Half were randomized to hear three songs while the other half heard instrumental-only versions of these same songs.

Participants reported decreases in stress and nervousness and increased relaxation after listening to either set of songs, and also showed decreases in blood pressure. So-as earlier studies have also suggested- quiet music at bedtime was indeed relaxing at the time. However, a quarter of the participants woke from sleep with an earworm, and the polysomnography data showed that instrumental versions of the songs were more likely to induce these awakenings as well as other sleep disruptions, such as shifts from deeper sleep to lighter sleep. Taken together, the findings represent “causal evidence for bedtime instrumental music affecting sleep quality via triggering earworms” the team writes.

Why instrumental-only songs should have a bigger impact than music with lyrics isn’t clear. The three songs used in this study were chosen because they were likely to be familiar. Hearing them without the lyrics might have prompted the participant’s brains to try to add the words, which might have made earworms more likely. If this is the case, all instrumental music may not have the same effect. However, the data from the first study is consistent with the idea that instrumental music generally is more of a problem.