When seeking the source of a mysterious malaise, few people would think to blame ions trapped in their mattress coils or cyclotronic resonance from the electrical system.

But if they did, they'd find products already on the market to allay their symptoms.

Targeting Americans concerned about exposure to mobile phone and electrical infrastructure, online retailers are selling a growing selection of protective gear. Listings include radiation-blocking boxers, radio curtain shields and pendants for removing electromagnetic frequencies.

"It seems that as our environment becomes more electrified, and we have more wired and wireless devices ... people are becoming more sensitized," said Emil DeToffol, president of online retailer LessEMF in Albany, New York.

DeToffol says sales of protective gear are up. Top sellers include meters for measuring magnetic fields and radio frequencies as well as clothes that shield wearers from electric, radio and microwave emissions.

Gear for frequency-sensitive individuals isn't a new idea. The concept of the tinfoil hat dates back decades. Equipment to reduce radiation from mobile phones has been around almost as long as mobile phones themselves.

But the proliferation of cellular antennae and electricity-sucking gadgetry is heightening concern among those who profess to suffer from electrical sensitivity, an illness triggered by exposure to frequencies emitted by various manmade technologies.

While some scientists believe the ailment's roots are more psychological than biological, retailers are finding a lucrative niche.

"Most people don't realize they're sleeping on a system that attracts EMF," said Rick Cabados, founder of the retailer HealthStores.com and its subsidiary, BlockEMF, which sells EMF Bed Shields, among other protective gear. Cabados says springs inside mattresses attract stray ions emitted from electrical outlets.

Other products purport to mitigate the effects of cyclotronic resonance, a process BlockEMF contends transfers energy from electrical wiring into the nervous systems of people within a home.

New inventions are also in the works. In September, two California men won a patent on a device that could be incorporated in a baseball cap to block radiation from a wireless antenna. Last year, a Taipei inventor patented an electromagnetic-waveproof bra cup.

But Ruth Douglas Miller, chair of the IEEE Engineering in Medicine and Biology Society's Committee on Man and Radiation, says scientific evidence does not support claims that signals emitted by everyday devices are harmful.

"The signals for everything from AM radio up to cell phones and microwaves are really really small," Miller said, noting that electromagnetic energy from natural sources, such as the sun, is much stronger.

Miller's committee maintains studies on electromagnetic hypersensitivity to date have been "overwhelmingly unsuccessful" in linking reported symptoms to electric or magnetic field exposure. The group also warns that many devices on the market falsely claim to reduce RF exposure from cell phones. The Federal Trade Commission has brought charges against some device makers.

DeToffol says he too has seen EMF-blocking products on the market that warrant skepticism. Key warning signs, he said, include questionable scientific explanations of how the product works and marketing that relies on subjective claims.

"That's a real tipoff -- when you see lots of testimonials," he said.