UV, X-rays, and gamma rays: equal per-photon hazard?

Ultraviolet, X-ray and gamma radiation are all understood to cause damage to biological tissue. On a per-photon basis, do all three types present an equal potential for tissue damage, or is a single gamma-ray photon capable of causing much more damage than a single UV photon, due to its far higher energy content?

Gamma rays and X-rays* do more damage because of their greater energy per photon, as you suggest. For one thing, UV rays don’t go through the body, and so can’t influence things well inside. X-rays and gamma rays can. Much heavier shielding is needed. But you can prevent UV light from harming your eyes by simply closing your lids.

  • (their wavelength regimes overlap, mainly because the terms distinguish more between origins than wavelengths)

Wouldn’t some gamma rays be too high energy to interact with the body at all?

Good point. From the Wikipedia article on gamma rays:

Radioactive decay (fission) commonly produces these energies.

The radiation length for high-energy photons is about 36cm, meaning that a photon will deposit roughly half its energy when going through somebody’s body. Photons don’t start getting “better” at higher energy, but they do get less harmfull per MeV, since at lower energies all of the photon’s energy can be deposited.