As an amphibian humanoid species from Qerr'Balak, Skrell have a number of physical distinctions from other species.
Skrell are humanoids with a height ranging from 5'10" to 6'2", females being generally taller than males. Amphibians coming from the warm, humid swamps of Qerr'Balak, their ectothermic bodies still carry several characteristic of water-dwelling species: their feet and hands are webbed,to various extents from one person to another and their respiratory system is a complex combination of vestigial cutaneous breathing, lungs, and gills placed at the back of the neck and protected by a set of three limp appendages commonly called headtails. Their bones are desner and more flexible than human ones, making them less likely to break under shock. Their blood contains hemocyanin instead of hemoglobin, giving it a dark blue colour when exposed to oxygen. A Skrell's life expectancy ranges from 100 to 120 years, depending on various factors.
The Skrellian life cycle starts as a tadpole, hatching from eggs a male Skrell fertilises with internal reproductive organs. During the next six to nine months, said tadpole will grow and develop its adult limbs, along with gills and headtails during the later stages of development. During this phase, the Skrell is forced to live underwater, and is very vulnerable: illness, environmental changes, and even the most minor wound will brutally disturb the tadpoles growth. Out of the fifty spawn generally birthed at the same time, it is rare that more than five of them survive to infancy. The transition to their next stage of growth is progressive. The Skrell is around 30 centimetres long at this point and doubles in size over the next month. Underwater, the gills start functioning to compensate for a now insufficient cutaneous respiration system, and their now-developed lungs allow them to take its first steps on land. Once past the tadpole stage, the Skrells growth is far slower, reaching proper adulthood after twenty years, with no further radical change to their physiology.
A Skrells skin can have a large variety of colours, ranging from dark blues and vivid reds to bright greens and jet black , with shades of various shapes across the body. It is slightly translucid in areas, mostly on the headtails, and exudes a thin layer of slime making the Skrell appear somewhat gelatinous at first sight. This slime has the added benefit of protecting the sensitive skin of a Skrell, preventing minor injury and irritation from chemical and gaseous substances out of the water. Despite being insufficient to fully supply the Skrell in oxygen, their skin still retains its respiration capabilities: should one of the lungs fail, the Skrell can normally function, albeit with some difficulty. While they are used to heavy pressures like on their homeworld, the fragile organ that is their skin makes them extremely vulnerable to lower ones; in tolerable amounts, it will only lead to large hematomas while lower pressures will inevitably lead to external and internal haemorrhages and air embolism, causing far more damage faster than a human would suffer. It also allows chemicals to travel easily through the skin, making Skrell somewhat vulnerable to cutaneous contact with chemicals; many drugs developed in Skrellian culture are used that way. The Skrell's sense of touch is overall more sensitive than a humans, but also more crude, lacking in detail.
Skrellian heads are comparatively simpler than human ones. In place of a nose are simple slits, lips are almost nonexistent and while it has as many facial muscles most of them are located in the lower area significantly decreasing the Skrells ability for facial expressions. Skrellian ears also lack an auricle, its function being taken over by a complex inner canal. Their eyes are far larger than human's, generally occupying half their face and entirely black when observed from the outside. Their size and their position, being further apart than on human faces, gives the Skrell a broader field of view. They also allow the Skrell to see better underwater and in the dark, although they are very sensitive to bright lights and fast changes in luminosity. Skrell see colours more vividly, with blue being a predominant one and ultraviolets being partially visible. In addition to the eyelids, the eyes are also protected by a nictitating membrane, most often seen when the Skrell is underwater. Skrellian hearing is, in most regards, far superior to humans. Their hearing range is close to a dog's, and while they have more difficulties to identify the location of a sound, they do not suffer from a decrease in ability under water. While their sense of taste is very delicate, allowing them to detect potential dangerous substances in their food, their sense of smell is underdeveloped, both lacking in sensitivity and scent distinction. Their vocal cords, accompanied by internal vocal sacs, give them a very large range of pitch, the upper levels being inaudible to humans.
The aforementioned headtails vary in size, being longer on females. A thinner skin allows the veins to be seen, much like hands. Their biological purpose is to protect the gills from external aggression, such as dust and microbes when outside of water. The sterile, dark and humid area quickly led female Skrell to store their fertilised eggs between the neck and the headtails, the slime preventing them from falling off except in case of violent movements. Later in their history, Skrell started decorating their headtails with jewellery and various decorations, despite this practice sometimes leading to infections near the gills.
The Skrell's physical appearance leads to the more xenophobic elements in human societies calling them frogs, salamanders, squidheads, and other less pleasing names, although the Skrell pay little attention to these remarks born of ignorance and false assumptions.
The Skrell are vegetarian, as indicated by their large, molar-like teeth. Not only are they unable to absorb animal protein, but doing so is likely to get them sick and nauseous, with food poisoning being possible if meat is ingested in too large quantities. Skrellian traditional foods are heavily based on the fungi-like organisms found on Qerr'Balak, with prepared food being the average meal for the common populace.
Despite an extremely low resistance to alcohol, Skrell have otherwise developed a high tolerance to a large amount of chemical substances, a result of their homeworld's flora being generally poisonous as a defence mechanism. Consequently, Skrellian food, and many of their medicines and herbal remedies, are generally too harmful for human consumption.