The order in which a needle would pierce your forearm is epidermal, dermis, and subcutaneous layers. The epidermal layer is the first layer of skin that you see if you were to look at your arm. It’s made up of skin cells called keratinocytes that produce a top protective barrier or shield for our body from any invading organisms such as bacteria or viruses. These cells are constantly being replaced every few weeks by new ones from below the surface of the skin. The next layer down is called the dermis and it provides strength and elasticity to our outermost layer of skin.
It also contains nerve endings that give us feelings like touch, pain, heat, cold etc., depending on how deep the needle pierces. The dermis also contains sweat glands that produce perspiration to help cool the body and regulate its temperature, hair follicles where our hair grows from, blood vessels and lymphatic channels which are a part of the immune system so they can fight off any invaders in order for us not to get sick or diseased. Finally we have the subcutaneous layer that is actually just below (sub) or under (cutea/scutis) the skin on top of muscle tissue such as your biceps muscles. The purpose of this layer is mainly fat storage cells like adipocytes but it also helps insulate our bodies against extreme temperatures by trapping heat around these cells to keep them warm during winter time. The