There is a lot of misinformation out there about bruises.  A lot of products make magical claims and recommendations not founded in science.

First off, what is a bruise?  A bruise is simply blood that is not in a blood vessel.  Blood in your body is like water in your house.  It is great to have water in your house, so long as it stays in the pipes!  Blood is the same story.  The analogy works well.  Leaked water stains your house, leaked blood stains your tissues (bruising).  Leaked water promotes growth of microbes (mold), leaked blood can promote infection.  Leaked water causes materials to swell, leaked blood causes tissues to swell (inflammation).  

Once blood has escaped the blood vessel, the “cat is out of the bag”.  You will get a bruise.  If the “leak” is deep, it may not be visible right away since it may take some time to “soak through” to the surface, but it will.  No amount of prevention after the fact will change that.  Once escaped, the red blood cells are effectively dead.  They will soon break down, their cell walls open, and their contents will be released.  Your body will respond by sending in inflammatory cells to clean up the mess, but along with this will come inflammation.  The released contents of the cells include hemoglobin which is the purple stuff.  The free hemoglobin moves more easily through the tissues and you see the bruise grow or come to the surface.  The hemoglobin deteriorates and is broken down into its metabolites which is when you see the green and yellow phases of a bruise.

BRUISE PREVENTION

The most important thing to prevent bruising is to KEEP THE RED BLOOD CELLS IN THE BLOOD VESSELS!  So simple, right?  Sadly, easier said than done, but you can certainly minimize the leakage.  When a needle is passed into the skin, it passes by and perhaps through blood vessels.  Some vessels are big enough to see, but most are not, so you can’t just ask your doctor to stay away from them.

PRE-ICING:  If you pre-ice the area it will temporarily reduce blood flow to the tissue.  This will have two important results.  1) The vessels will physically shrink, reducing the chance of the needle striking a vessel.  2) Should a vessel be nicked, it will have less flow through it, reducing the amount that leaks out.  And as a side benefit, pre-icing will deaden nerves and make it hurt less.

AVOID EXERCISE BEFORE A TREATMENT:  Exercise (or being hot in general) triggers a response in your body to open up blood vessels to the skin facilitating the release of heat.  Your skin is acting like a car radiator.    So, if your body in general is good and cooled down, there will be much less blood flow to the surface and less risk of bruising when a needle enters.

AVOID ALCOHOL BEFRORE A TREATMENT:  Alcohol also dilates superficial blood vessels.  

IMMEDIATELY APPLY PRESSURE: Applying pressure to the point of an injury will reduce blood that leaks out of injured vessels.  It is quite obvious how this works when you have an injury on the surface that is bleeding, the same holds true for bleeding under the surface.  This is one of the main benefits of using pressure dressings after surgery.  The bleeding below the surface will stop in a time frame similar to a surface injury of the same severity.  

Various anti-bruising formulas you might see advertised pretty much don’t work.  As mentioned, bruising is leaked-out blood, and pineapple juice or arnica don’t stop the physical act of blood leaking out of blood vessels.  Of course, having a good diet in the long term will promote healthy blood vessels and reduce the chance of injury.

IMMEDIATE AFTER CARE

Continuing to ice after the treatment will help slow blood leakage from any injured vessels by reducing flow.  For minor injuries, it will take minutes, perhaps an hour for any vessel wall injuries to be sealed up by your natural clotting mechanisms.  So icing is typically only of value after minor procedures for a short spell.  After more major events, 12, perhaps 24 hours of icing will be helpful.

LATE AFTERCARE

The cat is now out of the bag, so what can you do to speed up the elimination of the leaked-out blood and stained tissues.  Warm compresses starting 24 to 48 hours after the injury will open blood vessels facilitating the flow of healing cells (like macrophages) and increase the overall rate of fluid that moves through the tissues carrying away the stain.

Laser treatments can facilitate the absorption of the remnants of the escaped blood cells.  These work by pulsing high intensity light into the tissue that is of a complimentary wavelength to the color of the bruise.  The blood cell remnants absorb the light and because of the speed and intensity of the resulting temperature change, the remnants tend to break up into smaller pieces and are more easily removed.  This is similar to the concept of shattering glass if you suddenly pour super-hot water onto it.

BROWN DISCOLORATION AFTER A BRUISE

This is hemosiderin.  Hemosiderin is a breakdown product of hemoglobin and its iron component.  For whatever reason, some people are prone to this.  Thin delicate tissue like lower eyelids are also more prone to it.  Hemosiderin in the legs of people with vascular insufficiency should not be lumped in with hemosiderin staining in the face from a single injury.  In the former, the problem that caused the hemosiderin is still there so getting rid of it is unlikely.  Unfortunately, treatments for removing the staining in a timely fashion aren’t all that good.  Ultimately, most hemosiderin staining goes away on its own, but it may take a year.  Topical bleaching cream (hydroquinone) may help, but I don’t see it work.  Hydroquinone acts on pigment cells (melanocytes) which are not involved in hemosiderin staining.  Laser treatments have a better chance of working, particularly laser treatments designed for tattoo removal.