Great things are expected of terahertz waves, the radiation thatfills the slot in the electromagnetic spectrum between microwaves andthe infrared. Terahertz waves pass through non-conductingmaterials such as clothes , paper, wood and brick and socameras sensitive to them can peer inside envelopes, into livingrooms and "frisk" people at distance.

The way terahertz waves are absorbed and emitted can also be used to determine thechemical composition of a material. And even though they don't travelfar inside the body, there is great hope that the waves can be used tospot tumours near the surface of the skin.

With all that potential, it's no wonder that research on terahertzwaves has exploded in the last ten years or so.

But what of the health effects of terahertz waves? At firstglance, it's easy to dismiss any notion that they can be damaging.Terahertz photons are not energetic enough to break chemical bonds orionise atoms or molecules, the chief reasons why higher energyphotons such as x-rays and UV rays are so bad for us. But couldthere be another mechanism at work?

The evidence that terahertz radiation damages biological systemsis mixed. "Some studies reported significant genetic damagewhile others, although similar, showed none," say BoianAlexandrov at the Center for Nonlinear Studies at Los Alamos NationalLaboratory in New Mexico and a few buddies. Now these guys think theyknow why.

Alexandrov and co have created a model to investigate how THzfields interact with double-stranded DNA and what they've found isremarkable. They say that although the forces generated are tiny,resonant effects allow THz waves to unzip double-stranded DNA,creating bubbles in the double strand that could significantlyinterfere with processes such as gene expression and DNA replication.That's a jaw dropping conclusion.

And it also explains why the evidence has been so hard to garner.Ordinary resonant effects are not powerful enough to do do this kindof damage but nonlinear resonances can. These nonlinear instabilitiesare much less likely to form which explains why the characterof THz genotoxic
effects are probabilistic rather thandeterministic, say the team.

This should set the cat among the pigeons. Of course, terahertz waves are a natural part of environment, just like visible and infrared light. But a new generation of camerasare set to appear that not only record terahertz waves but also bombard us with them. And if our exposure is set to increase, the question thaturgently needs answering is what level of terahertz exposure is safe.

Ref: arxiv.org/abs/0910.5294:DNA Breathing Dynamics in the Presence of a Terahertz Field