[2] Generally speaking, the ectoderm differentiates to form epithelial and neural tissues (spinal cord, nerves and brain).

This includes the skin, linings of the mouth, anus, nostrils, sweat glands, hair and nails,[3] and tooth enamel.

Heinz Christian Pander, a Baltic German–Russian biologist, has been credited for the discovery of the three germ layers that form during embryogenesis.

Pander's work of the early embryo was continued by a Prussian–Estonian biologist named Karl Ernst von Baer.

Baer took Pander's concept of the germ layers and through extensive research of many different types of species, he was able to extend this principle to all vertebrates.

Baer published his findings, including his germ layer theory, in a textbook which translates to On the Development of Animals which he released in 1828.

At the start of this process, the developing embryo has divided into many cells, forming a hollow ball called the blastula.

[2] Like the other two germ layers – i.e., the mesoderm and endoderm – the ectoderm forms shortly after fertilization, after which rapid cell division begins.

[2] Likewise, while the surface ectoderm becomes the epidermis,[6] the neuroectoderm is induced along the neural pathway by the notochord, which is typically positioned above it.

The cells continue to extend inward and migrate along the inner wall of the blastula to form a fluid-filled cavity called the blastocoel.

At the same time, when this thin layer of dividing cells reaches the dorsal lip of the blastopore, another process occurs termed convergent extension.

[2] All of the organs that rise from the ectoderm such as the nervous system, teeth, hair and many exocrine glands, originate from two adjacent tissue layers: the epithelium and the mesenchyme.

This aspect represents a major handicap particularly in the summer, limits the patient's ability to participate in sports as well as his working capacity, and can be especially dangerous in warm climates where affected individuals are at risk of life-threatening hyperthermia.

Facial malformations are also related to HED, such as pointed or absent teeth, wrinkled skin around the eyes, a misshaped nose along with scarce and thin hair.