The primary beam hazards associated with Class IV lasers consists of eye and skin
injuries. The most severe eye injuries are caused by viewing the beam either directly
or through specular reflection. At an infra-red wavelength of 
most of the
laser light entering the eye is absorbed in the retina. The primary adverse effects
from direct or specular viewing are blindness and severe retinal burns. The primary
adverse effects from accidental viewing are retinal burns. The retina is most
sensitive to radiation of this wavelength, and if the laser energy incident to the eye
is too high, it can cause an irreversible retinal burn.
Laser radiation of the intensity associated with Class IV diode lasers can also cause irreversible damage to the skin. The damage caused is either associated with temperature rise of the skin tissue following the absorption of laser energy (skin burns) or with surface reactions resulting from photon interactions at the molecular level (photochemical effect), disrupting the normal functionality of the skin tissue.