Ask most healthcare providers what to do for a bruise and you’re likely to get a dazed look. Modern medicine really doesn’t have any FDA-approved treatments for this common problem.

Ask a grandmother, though, and you just might learn about some remedies that work.

Over the years, the most popular bruise remedy we’ve heard about seems to be topical applications of castor oil. The castor bean (Ricinus communis) was known and used for remedies as far back as the ancient Egyptians.

In past centuries in this country, a castor oil pack was a popular treatment for sore joints or muscles. Several layers of flannel would be soaked in castor oil, then placed over the injured part of the body.

A hot-water bottle would then be placed over it for half an hour or so. This was supposed to ease pain.

Topical castor oil has also been used to prevent or heal bruises. One person wrote to us about a boxer who applied castor oil after every match to prevent hematomas and bruising. A lacrosse player has also testified to its effectiveness for this purpose.

“My mother-in-law uses castor oil for bruises. At Christmas, my sister-in-law sat down in a very heavy old rocker-recliner chair. It went crashing to the floor, and one corner landed right on top of my mother-in-law’s foot.

“My sister-in-law was dazed and took a moment to get up, which meant my mother-in-law’s foot was trapped under the chair for a few seconds. We all urged her to go to the hospital to make sure no bones were broken, but she refused. Instead she slathered the top of her foot with a generous amount of castor oil. She said that castor oil applied immediately to a bump reduces swelling and prevents bruising.

“I didn’t believe it until the next day when I saw that her foot was fine! I don’t advocate castor oil for serious injuries, and I do think my mother-in-law should have had her foot X-rayed, but for minor accidents, it works great!”

Castor oil contains ricinoleic acid. This compound has both pro- and anti-inflammatory effects (European Journal of Pharmacology, Oct. 27, 2000; Naunyn-Schmiedeberg’s Archives of Pharmacology, Aug., 2001). Regular topical use might improve pain tolerance, but no one has studied an anti-bruising effect.

Another time-honored topical treatment for bruise prevention comes from a plant called Arnica montana, or arnica for short. It grows in mountainous parts of Europe and the flowers have long been used to treat skin problems.

Because arnica contains toxic compounds called pyrrolizidine alkaloids, it should not be taken internally.

Nowadays, there are a number of ointments, lotions, and gels that contain extract of arnica. The compounds from this plant may stimulate the immune system and appear to prevent blood clots from forming. That might explain why people find it helpful against bruising.

It has also been used for sprains and painful joints. Some people use it for muscle pain, but one randomized, placebo-controlled, double-blind trial found that topical arnica actually increased muscle pain after exercise instead of relieving it (Annals of Pharmacotherapy, Oct., 2010).

“Yesterday, I had a tumble off my bike onto my knees on the way home. They were bruised, but I was able to pedal home and get arnica gel on them in about ten minutes,” said a reader.

“My mother swears by this herb, but I have not had occasion to use it much. I applied more gel before bed and again in the morning.

“Today, one knee shows no effects of having been bruised, and the other is not black and blue and barely hurts at all. I am stunned by the effectiveness of arnica.”