Bruises do not break the skin as wounds do, but they do damage underlying tissues. Bruising causes pain and swelling, and the affected area turns purple after a while. Bruises are not a big deal as long as the blow that causes them is not too violent. While traveling, especially with younger children, always expect there to be bumps or painful bruises. It is in these cases when you should use arnica, whose active ingredients provide instant relief.
For external use, arnica is recommended when there is local inflammation brought on by a concussion. It works by lessening the bruises and blood clots that accumulate under the skin. It should be applied to the injured area as soon as possible, in diluted doses for people with sensitive skin, as it can be irritating and cause allergic reactions. It should never be applied to open wounds. If used for a prolonged period, it can cause swelling and sores on the skin.
Arnica is available as a powder, tincture, and oil, which are used to prepare ointments, plasters, or creams, and then applied to the affected area three times a day. It can also be found in liquid extract and as dry and crushed plant ready for making infusions.
Besides being an effective treatment for shock, arnica alleviates muscle tears and frostbite, as well as inflammations caused by rheumatism. It is recommended for external use only.
Sources: Medicinal Plants at Home