Just curious as to how many layers of skin the human actually has (spot the person who didn't pay attention in Biology class! )

There are 3 layers of skin. They are called the Dermis, Epidermis and Subcutis.

The epidermis is divided into 5 layers. The basal layer contains the basal or mother cells that ensure continual regeneration of the skin through cell division. Above lie the cells of the prickle cell layer . Next come the granular, clear and horny layers . The horny layer consists of 15 - 20 cell layers that, together with the epidermal lipids, form the permeability barrier. This performs two important functions:

It hinders the invasion of certain substances such as microorganisms, chemical irritants and allergens.

It minimizes transepidermal water loss and so is of great importance to the body.

The dermis is divided into two layers, the stratum papillare forming the distinct undulated border with the epidermis and the stratum reticulare, which continually merges into the subcutis. The main constituents of the dermis are the proteinous connective tissue fibres which are connected to the glycosaminoglycans or mucopolysaccharides.

The epidermal appendages include the nails, hair, and skin glands . Especially the sweat and sebaceous glands play an important role in formation of the hydrolipid film.

The subcutis serves foremost as the energy reservoir of the skin: here nutrients in the form of liquid fats are stored in the adipocytes. At the same time, the subcutis provides insulation and shock absorption.

Which skin layer can be damaged by sunlight?

The first layer or what we call the top part is mostly damaged by sun light. The 2nd and 3rd layers can only be damaged by burn, strong ultraviolet rays and laser.