[thedoc (OP)]

ValeriePollack asked the Naked Scientists:
   Could the battery in a wrist watch,which always covered a mole on my left wrist,cause that mole which had been there for years to become a malignant melanoma.The melanoma has been removed by wide excision.Surgeon told me of research going on in the long term use of battery powered cellphones etc.I have bi-lateral hearing aids also battery powered.
What do you think?

[chris]

I think that a more plausible explanation is as follows:

Wearing a watch tends to shield the underlying patch of skin from the Sun's rays, with the effect that this patch of skin is relatively less pigmented (melanised) compared with the surrounding, more exposed skin.

This means that, on occasions when the watch is not worn, the less-pigmented skin is more vulnerable to the effects of UV light exposure, leading to a higher risk of DNA damage in that area that might lead to melanoma.

It is also possible that this is entirely a coincidence, and that had a melanoma cropped up anywhere else on the body, no significance would have been attributed to wearing a watch or not.

[evan_au]

research going on in the long term use of battery powered cellphones

Research to date has shown no definite link between cellphone use and cancer.
Cellphones emit non-ionizing radiation, which should not cause mutations. But the use of cellphones is increasing, and rumors of the risks persist, so it is prudent to have ongoing studies.

wrist watch... bi-lateral hearing aids also battery powered

Cellphones are designed to emit radio frequency energy, with a range of 1 km or more. It can emit up to 0.1W, which is why you need to recharge them every day, despite the very high power capacity of rechargeable Lithium ion batteries.

Wristwatches are designed not to emit radiation. The older types usually ran off a 32kHz crystal, which can emit almost no radiation from its tiny circuit. The battery lasts a year or more. So the power levels involved are incredibly small.

In-between, hearing aids need their batteries changed perhaps once every week or so. They are low-power devices, often driven by zinc-air batteries. The more advanced models communicate wirelessly with each other, with a range of less than 1 meter. This power level is far too low to cause damage.

These all use different battery technologies; two of the battery types are hermetically sealed, and the third draws in oxygen, but emits no chemicals. So we can be pretty sure that the batteries on your person did not cause a problem.

The most likely cause is sunlight. It has a power of around 700W per square meter at sea level, and contains a significant amount of ultraviolet radiation, which is able to cause DNA damage. 

wrist watch always covered a mole on my left wrist

It seems that the wristwatch would have protected the mole from sunlight, to some extent.

A mole is an abnormal growth - something is not quite right. Another mutation may have turned it malignant.