Nutrition appears to be absorbed dermally, or possibly directly injected. It is commonly reported that the greys either soak themselves in a slurry solution, or enzymatic bath, or smear a peroxidated nutritional solution on their skin. This would explain their strange bodily odor, which has been described variously as like burnt wood, cinnamony, mentholated, or an electric-ozone smell. Skeletal structure is child-like, with spindly limbs generally elongated beyond human proportions. Genitalia also are reported as child-like or absent, in the case of the clone class.
Some greys appear to be genetically engineered replicants, with minimal internal organs.
The relatively thick epidermis appears translucent when drained of blood. This includes their skeletal structure which appears to be adapted to minimal gravitational weight, their general lack of pigmentation, and their large, black, almond eyes, which appear adapted to extreme light conditions. In comparison to human beings the greys exhibit enough similarities to conclude that they are somehow related to humans in evolutionary terms. This would infer that the greys have evolved along similar lines, in similar environments. Another possibility in this realm is that the greys are an older race who have lived here on Earth in vast underground chambers, interacting with humanity throughout history.