The skin has a total of 3 layers: the epidermis, the outermost layer of the skin, provides a waterproof barrier and also creates our skin tone as well. The dermis, beneath the epidermis, contains tough connective tissue, hair follicles, and sweat glands. The deeper subcutaneous tissue (hypodermis) is made of fat and connective tissue. All of these things are universal for every person but there all different types of skin types that vary with every individual.
Normal skin type: This type of skin is not too dry but also not too oily, normal skin has no or few imperfections, no severe sensitivity, barely visible pores, and radiant complexion.
Dry skin: Your skin can crack, peel, or become very itchy, irritated, or inflamed. If it's very dry, it can become rough and scaly, especially on the backs of your hands, arms, and legs. Dry skin could be caused or even made worse by your genes, aging or hormonal changes, weather, UV radiation from tanning beds, etc.
Combination skin type: Your skin can be dry or normal in some areas but also oily in others such as the T-zone (forehead, chin, and nose). Many people have this type but it may need minor different care in different areas. Combination skin can have pores that look larger than normal due the fact that they're more open. Blackheads and shiny skin are also some key things that comes with combination skin.
Oily skin: Oily skin happens when the sebaceous glands in the skin make too much sebum. Sebum is the waxy, oily substance that protects and hydrates the skin. Having oily skin can come from a variety of things such as genetics, over-washing, medication usage, cosmetics, hormonal changes, and poor diet.