Due to evolving in an environment with little disease before spending hundreds of years in a sterile environment, quarians have an almost non-existent immune system, causing what would be a negligible infection in one species to be lethal to a quarian.
The most distinctive quarian trait is their advanced enviro-suits. However, beyond the head and torso, quarians are much more similar to turians, having bowed legs, three thick fingers on each hand, and two similarly shaped toes on each foot. Quarians are superficially similar to humans in terms of facial structure, body composition, sexual dimorphism, hair, and height, though they are notably shorter and smaller.