For many people, the smartphone is ubiquitous, practically an appendage, playing a part in nearly every aspect of life. Want to avoid eye contact with strangers in the elevator? Check your email. Subway delayed? Slack a colleague. Splitting a bar tab with a friend? Tap on the Cash app. Even when it’s not in active use, the phone is there. It’s in our pockets all day long, and then it overnights on the night stand awaiting its alarm-clock moment.

This is a problem, according to state health authorities in California, who issued a warning this week about exposure to radio-frequency energy emitted by cellphones and any deleterious impacts that RF energy may have on human health. The warning, according to TechCrunch, came on the heels of the court-ordered release of a 2009 document that discussed theorized but unproven links between RF energy and such serious health concerns as brain cancers, reduced sperm counts and learning impediments.

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TechCrunch quoted California Department of Public Health Director Karen Smith as saying: “Although the science is still evolving, there are concerns among some public health professionals and members of the public regarding long-term, high use exposure to the energy emitted by cell phones.”

The state health department this week recommended that those wishing to limit exposure to RF energy keep phones away from their bodies; reduce cellphone use when the cellular signal is weak or while in a fast-moving vehicle, when a device may emit elevated RF energy as it attempts to maintain connectivity; avoid holding a device to the ear for prolonged periods and remove headsets when not on a call; keep phones away from the bed at night; and limit the use of mobile phones to stream content or download and upload larger files.