Heres a more technical description from the web:
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Arnica is also commonly called leopard's bane. The arnica plant has a bright yellow, daisy-like flower that blooms around July. Preparations made from the flowering heads have been used in homeopathic medicine for hundreds of years. It is popular in Germany and over 100 drug preparations are made from the plant. Arnica is a perennial that is protected in parts of Europe.

The active components in arnica are sesquiterpene lactones, which are known to reduce inflammation and decrease pain. Other active principals are thymol (an essential oil), flavonoids, inulin, carotenoids and tannins.

Arnica works by stimulating the activity of white blood cells that perform much of the digestion of congested blood, and by dispersing trapped, disorganized fluids from bumped and bruised tissue, joints and muscles.

Arnica is known to stimulate blood circulation and can raise blood pressure, especially in the coronary arteries. The plant is used externally for arthritis, burns, ulcers, eczema and acne. It has anti-bacterial and anti-inflammatory qualities that can reduce pain and swelling, improving wound healing.

Part Used: Extract of the blossoms

Common use: It is typically rubbed on the skin to soothe and heal bruises, sprains, and relieve irritations from trauma, arthritis and muscle or cartilage pain. Applied as a salve, arnica is also good for chapped lips, irritated nostrils and acne.

Also found some good 'cautionary' advise on the web....(promise to stop now :)
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The herb's active ingredients also have mild pain-relieving, anti-inflammatory, and antibacterial actions. One of arnica's primary components, helenalin, also has a strong anti-edemic (anti-swelling) effect. Given these qualities, it's little surprise that traditional healers recommend applying a cold compress soaked in tincture of arnica to reduce bruising.

Historically, herbalists used arnica to prepare teas and tinctures they believed would benefit a wide range of ailments, from anemia and depression to heart disease. But it was eventually discovered that even small amounts of arnica (except for super-diluted homeopathic formulations) can irritate mucous membranes, cause vomiting and diarrhea, and lead to drowsiness.

Although arnica is poisonous when taken internally, it is used in highly diluted homeopathic formulations. In these tiny tablets or pellets, which are dissolved under the tongue, the arnica has been diluted literally hundreds of times, so at homeopathic levels poisoning is virtually impossible. Recent studies have cast doubt on the remedy's effectiveness, however. A 1998 Archives of Surgery review of placebo-controlled clinical trials of homeopathic arnica concluded that on balance, there is no solid evidence that arnica offers any real benefit. The authors further noted that the more scientifically rigorous, or best-designed, studies tended to show the negative findings.

Arnica is also used in more than 100 cosmetic formulations that appear in a wide range of products, including hair tonics, anti-dandruff products, and perfumes. A 2001 article in the International Journal of Toxicology reported that so far, there is not enough data to assess the safety of using arnica in cosmetics.

Specifically, topical arnica is most commonly used for:

* Muscle strains and sprains. Arnica is widely applied to ease the inflammation and pain of muscle strains and sprains caused by overuse or injury. Although results have been contradictory, some studies concluded that for a short period immediately following a marathon run, arnica reduced muscle soreness. The effect was only temporary, however.

* Arthritic joints. Inflamed and painful joints are said to benefit from arnica as well. Using the herb in a hot, moist compress may be helpful for arthritis pain, though it is not known whether it is simply the heat or the arnica that provides the relief.

* Psoriasis and eczema. Numerous herbal formulas for these persistent skin disorders contain extracts of arnica, which may help given its anti-inflammatory and numbing qualities.

* Insect bites. Because of its anti-inflammatory and antiseptic effects, topical arnica is believed to reduce the swelling and pain caused by insect bites. It may also help prevent infection.



Forms

* tincture
* spray
* ointment
* oil
* liquid
* gel
* cream

Dosage Information

Special tips: --If you'd like to try topical arnica, for the greatest effectiveness look for an arnica cream containing approximately 15% arnica oil.

* For muscle strains and sprains: Apply arnica cream, gel, or ointment every 3-4 hours to the affected area.

* For arthritic joints: Apply arnica cream, gel, or ointment every 3-4 hours to the affected area.

* For psoriasis and eczema: Use the cream form of arnica; apply to affected area twice daily.

* For insect bites: Use cream or ointment; apply every 3-4 hours as needed to relieve symptoms.

Be sure to check out our Dosage Recommendations Chart for Arnica, which lists therapeutic dosages for specific ailments at a glance.

General Interaction

There are no known drug or nutrient interactions associated with arnica when applied topically.

Possible Side Effects

When used frequently or for long periods, arnica can cause contact dermatitis or eczema.

Cautions
* Don't take arnica internally except in accepted homeopathic dosages. As little as 1 ounce of arnica tincture taken orally can cause shortness of breath, raise blood pressure, and damage the heart. High doses can be fatal.
* Don't apply any form of arnica to broken or bleeding skin.
* As with any herbal remedy, arnica can cause an allergic reaction, a rash called contact dermatitis, when it's applied to the skin. Avoid this herb if you are sensitive to arnica or to any plant in the daisy family.
* Be sure to use only the recommended amount of topical arnica. If too much is applied, or if it's used for too long, topical arnica can cause redness, swelling, itching, and blisters.
* Some sources recommend using a diluted arnica tincture or tea as a gargle for reducing sore throat-related inflammation. If you choose to use arnica in this way, be extremely careful not to swallow it. Safer alternatives are certainly available.

Got the pillets couldn't use cream as Blue's paw is still bandaged - Instructions: 1 pill to be sucked when required. How the hec do you get a dog to suck a tablet

Just let him eat it and hope for the best. It seems to be helping. Stopping him going mental in the garden is really tricky esp after he has been stung for trying to eat a wasp oh and peeing on one

Amanda