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Your skin has three different layers. These are called (going from outside to inside) the epidermis, dermis, and subcutaneous layers.
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The outer layer of your skin (epidermis) is formed of mainly dead cells on the surface, and it can range from about 0.1mm (the size of a human hair) in thickness to 1.5mm thick.
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Little cuts heal well, however, if the skin is hurt really bad, it can form scar tissue. Scar tissue is not like normal skin - it doesn't have sweat glands or hair, and is usually a different color than the rest of your skin.
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A colored ink-like substance (a pigment) called melanin determines how dark or light your skin is. Skin with lots of melanin is dark, while a small amount of melanin produces lighter skin. Melanin helps protect your cells from sun damage.
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A callous forms when you rub or put pressure constantly on one area of skin. A callous is just thick, tough skin that helps protect you from damage. Look at the hands of someone who plays the guitar, as they will often have lots of callouses on their hands!
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You know all that dust in your house? A very large amount of that dust is actually dead skin!
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The process to make the very top part of the epidermis starts at the bottom part of the epidermis, where new skin cells are being formed. As they form, they push up, and the older dead layer on top rubs off. It takes about 2 weeks to a month normally for a newly formed cell to die and reach the top part of the epidermis.
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Every minute of every day of your life, you lose 30,000 to 40,000 dead skin cells from your epidermis. This equals about 9 pounds of dead skin cells every year!
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The middle layer of skin, or the dermis, is hidden under the epidermis. It is where sweat starts from (sweat glands), and is also where your nerves and blood vessels are.
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Some of the nerves in your dermis aren't connected directly to your brain; they connect to your muscles instead. This way, if you feel something painful, these nerves feel it, and send a signal to your muscles (though the spinal cord) to remove your hand or feet. This happens in a split second, and you don't even have to think about it!
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The bottom layer of skin, called the subcutaneous layer (or hypodermis) is mostly fat. It is also where your hair starts from (in hair follicles). This layer absorbs shock, like if you bump into something. It is also what attaches your skin to all the tissues underneath!
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You have hair follicles all over your body, except in a few places - your lips, palms of the hands, and soles of the feet. On your head alone, you have more than 100,000 hair follicles!
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