The recording electrodes can be carried by a skull cap, and nothing has to penetrate the skin.

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It is unclear whether the antioxidants in grapeseed oil penetrate the skin sufficiently to benefit the skin, dermatologists say.

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Efforts to make the particles smaller have worked, but have raised safety concerns because they can penetrate the skin and potentially interact with cells.

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"We are hypothesising that having these genes expressed in the epidermis will provide a first line of defence as insecticides penetrate the skin, " he explained.

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But a product's SPF indicates only its ability to defend against sunburn-causing ultraviolet-B rays and not against ultraviolet-A, which penetrate deeper into the skin and cause premature aging. (Both types contribute to skin cancer.) For example, a person wearing SPF 50 could spend considerable time in the sun without getting burned.

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One zaps the passenger with a tiny amount of X-rays that penetrate the clothes, but stop at the skin.

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And so -- but apparently the ones that are being tested right now by all the big laboratories, they only can be used for skin cancer or places where the light can penetrate fairly close to the surface.

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Skin that has hardened, sometimes to the point where needles can't penetrate it, will not reverse itself, either.

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