When is a bruise just a bruise and when is it cause for worry? Dr Edward Cherubino explains what makes our skin change colour and swell in case of injury.

Whether falling off a bike, bumping against a table or getting hurt while playing sports, we have all sported a bruise at some point in our lives. But what exactly makes the skin mark that way?

Bruising occurs when tiny blood vessels are broken as a result of a hit to the skin; blood leaks from these damaged blood vessels into the surrounding layers of the skin, giving rise to a bruise. Bruises are associated with pain; the blood collects under the skin, resulting in the building of pressure. Nerve endings within the affected tissue detect this increase in pressure, which is perceived as pain.

While people of any age can experience bruising, the injury required to produce a bruise varies with age. While it may take quite a bit of force to cause a bruise in a young child, even minor bumps or trivial grazes may cause extensive bruising in an elderly person. This is because the skin and the underlying blood vessels become more fragile as we age.

The amount of bruising experienced may also be affected by medications which interfere with blood clotting; blood thinning medication and steroids are two examples.

While most bruises are not a cause for concern, in some cases they may be a sign of an underlying medical condition. When the body suffers from a decrease in the number of platelets – which are the cells found in our blood – unexplained bruising can occur. It may also be a warning sign of serious medical conditions such as leukaemia; should this occur, seeking medical advice is a priority.

A rainbow of colours?

Bruises change in appearance over time and it may be possible to tell how old a bruise is by looking at it. When it first appears, a bruise will be reddish looking, reflecting the colour of the blood in the skin. After one to two days, the red-coloured iron from the blood will start to break down and the bruise will appear blue or purple. By day six, the colour changes to green and by day eight to nine, the bruise will take on a yellowish-brown tinge.

The bruised area will be repaired by the body in two to three weeks, after which the skin will return to normal. As the blood is broken down, the pressure in the affected area is reduced and the pain associated with the bruise decreases.

There are a number of things you can do to prevent or help minimise the amount of bruising that occurs after injury. Follow the RICE acronym for the most effective healing; rest, ice, compression and elevation. A bag of frozen peas is ideal, it is easily found in the home and provides the right amount of coldness, while also moulding to the shape of theinjured area. Wrap in a towel to prevent direct application to the skin, which can in turn cause frostbite. The cold constricts the blood vessels, which in turn reduce the blood flow to the affected area and as a result also reduce inflammation, swelling and pain.

Compression helps by allowing the injured part of the body to rest, while also decreasing blood flow to the injured area. Elevation works by reducing the amount of blood flowing to that affected area.

The lower the injury, the more blood will flow to that area, causing increased bruising and swelling. Rest is essential for rapid recovery. Patients who fall and sustain a bruise and who are on anti-coagulant medication should seek medical advice, especially if the injury involves the head or if the bruise increases in size.