Understanding skin function, skin healing, and bruising process

The skin is made up of three layers:

1. Epidermis: The outermost layer of the skin that protects the body from the environment. The thickness of the epidermis varies in different types of skin. On the eyelids, the epidermis is 0.5 mm thick, and 1.5mm thick on the palms and soles of the feet. The epidermis contains the melanocytes (the cells in which melanoma develops), the Langerhans’ cells (involved in the immune system in the skin), Merkel cells and sensory nerves. The epidermis regenerates itself approximately every 28 days; all cells are turned over as the most superficial cells are replaced by new ones.

2. Dermis: It is located beneath the epidermis and is the thickest of the three layers of the skin (1.5 to 4 mm thick), making up approximately 90% of the thickness of the skin. The main functions are to regulate temperature and to supply the epidermis with nutrient-saturated blood. Much of the body’s water supply is stored within the dermis. This layer contains most of the skins’ specialised cells and structures, including blood vessels, lymph vessels, sweat glands, sebaceous glands, nerve endings, and collagen and elastin.

3. Hypodermis: The innermost layer of the skin that consists of a network of fat and collagen cells. It functions as both an insulator, conserving the body’s heat, and as a shock-absorber, protecting the inner organs. The blood vessels, nerves, lymph vessels and hair follicles also cross through this layer.

Wound healing is the process by which the skin, or any injured organ, repairs itself after injury. The main aim of wound healing is to prevent or limit further damage, to clean and seal the wound against infection, to restore tissue strength, and if possible, tissue function.

The wound healing process is characterised by four overlapping phases:

1) An initial response to maintain normal skin function (homeostasis)

2) An inflammatory response to prevent infection

3) A proliferative phase to reconstitute the wound site

4) A remodelling phase where tissue strength and function are restored

A bruise shows up when an injury makes small blood vessels bleed under your skin. Your skin isn’t broken, so blood doesn’t have anywhere to go. It pools and forms clots and changes the colour of the skin above the injury.

Types of bruises include:

Contusions: Bigger bruises caused by harder blows to the skin

Ecchymosis: A flat, purple bruise that happens when blood leaks into the top layers of your skin

Haematoma: Lump under your skin formed by clotted blood. The area is usually swollen, raised, or painful. It is not the same thing as a haemorrhage which is a heavy bleeding inside or outside your body.

Bruise colour arises from the formation and accumulation of haemosiderin and biliverdin beneath the skin after bleeding. Bruises resolve as the body reabsorbs the blood. A fresh bruise, which can be tender to touch, appears as blue to reddish purple in colour due to the breakdown of haemoglobin and subsequent storage of released iron in haemosiderin. As healing progresses, the resolving bruise changes colour to yellow as a result of enzymes degrading biliverdin to bilirubin and fading until the bruise completely disappears.

Why do I bruise so easily?

  • Getting older: As you age, your skin gets thinner and loses the protective layer of fat that acts as a cushion when you bump into something. Also, your blood vessels get more fragile.
  • Some medicines and supplements: Aspirin or a blood thinner can cause occasional black-blue mark. Some supplements, like fish oil and ginkgo, can do the same.
  • Steroids like prednisone can also cause easy bruising because they thin the skin
  • Low vitamin C: If you don’t get enough nutrients, you may bruise easily.
  • Family history
  • Sun damage: Over time, the sun slowly weakens your skin and the tiny blood vessels underneath it.
  • Blood disorders usually cause symptoms other than bruising
  • Intensive exercise: You’re pushing your muscles with so much effort that it leads to tiny tears in your blood vessels.
  • Heavy drinking associated with cirrhosis
  • Some types of cancer such as leukaemia