The latest wellness trend and “sleep hack” involves switching off the bathroom light before stepping into the shower. In the dimness, the water feels louder, the day’s visual clutter fades and the hope is that sleep will come more easily. This practice, often called “dark showering”, has spread on social media, with people claiming that washing before bed in near darkness leads to deeper and faster sleep.

There is little research on dark showering as a standalone sleep technique. However, sleep science is clear about two key factors this ritual changes: light and heat. Both can nudge the body toward sleep or keep it alert.

Light is not only for seeing. Bright light in the evening signals to the brain’s internal body clock that it is still daytime. This delays the release of melatonin, a hormone that helps regulate sleep and is often described as the body’s “darkness signal”.

In a laboratory study of 116 adults, typical room lighting between dusk and bedtime reduced early night melatonin levels by about 70% compared with very dim light. Exposure to room light before bed also shortened the total duration of melatonin release by about 90 minutes. Participants reported feeling more alert.

Read more: Light at night can disrupt circadian rhythms in children – are there long-term risks?

Bathrooms are often the brightest rooms in a home. Overhead lighting and illuminated mirrors are designed for precision tasks that are useful in the morning but less helpful late at night. Turning these lights off, or dimming them, removes a strong signal that it is........

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