Nonpharmacological treatments, such as relaxation techniques or cognitive behavior therapy for insomnia (CBT-I), are recommended as complementary and alternative therapies. However, the associated side effects and dependencies present challenges to the long-term use of hypnotic drugs. Pharmacotherapy for insomnia has been widely employed. These results suggest that safe and easy inhalation of warm steam via a steam-generating mask improves psychological relaxation and sleep. Compared to the sham condition, steam inhalation before bedtime was associated with a higher EEG delta power density during the first third of sleep episodes and better subjective sleep quality in the morning. At bedtime, the subjects' subjective apprehension of the next day was reduced significantly under steam inhalation, compared with the sham condition.

In the morning, each participant was instructed to report their sleep details subjectively using a visual analog scale. During sleep, electroencephalograms (EEGs) were recorded using a single-channel portable device. We evaluated the participants' electrocardiograms and subjective moods while wearing the mask. The functional mask provided approximately 600 mg of steam for 10 minutes and maintained an interior temperature of 38–40☌ for 15 minutes. The participants were instructed to wear a warm steam-generating mask or sham mask over the nose and mouth for 15 minutes immediately before habitual bedtime and were then allowed to sleep until their habitual waking time. All experiments were conducted in the participants' homes.

The participants included 17 adult men with mild sleep difficulties and anxiety. This study aimed to examine the effects of warm steam inhalation before bedtime on subsequent sleep quality. However, the effects of warm steam inhalation on sleep have not been studied closely. In humans, the inhalation of warm steam has been reported to decrease the respiratory rate.

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