All About Arnica
Arnica (Arnica montana) grows in high mountain regions of Northern Europe, Siberia and is also cultivated in North America. The German folk name for arnica means “mountain of well-being.” Arnica montana is from the Asteraceae/Compositae family.
The Arnica montana plant grows one to two feet in height with vibrant flowers similar to daisies. Stems are round and hairy, ending in one to three flower stalks, with flowers two to three inches across. The upper leaves are toothed and slightly hairy, while lower leaves have rounded tips.
Arnica has been used for centuries medicinally to reduce pain and inflammation. The active components of Arnica montana include sesquiterpene lactones and flavonoids, which are known to reduce inflammation and ease pain. It also contains thymol, an essential oil component that fights infection, and carotenoid, a powerful antioxidant. The flowers are processed in an infusion to be used as carrier oil, while the roots of the plant are used for homeopathic remedies.
Medicinally, Arnica montana is available in many forms: infused oil, tincture, homeopathic ointment, cream, salve and pills.
Arnica Infused Oil is a wonderful addition to any first aid kit! You can use it on injuries, sprain, and bruises with unbroken skin. Arnica speeds up the healing process, prompting your body to send more white blood cells to clean up and repair the bruise.
Areas of pain and inflammation
Fractures and sprains
Strained muscles and tendons
Add to massage blends
Pain Relieving Blend In 1 oz. Arnica (Arnica montana) infused oil add: 5 drops Helichrysum (Helichrysum italicum) 4 drops Lavender (Lavandula angustifolia) 4 drops Palmarosa (Cymbopogon martinii) 5 drops Ginger (Zingiber officinale)
Shake well and use a small amount as needed. If not in use it is best to refrigerate to extend the shelf life. This is a 3% dilution blend and should be reduced to 1% during pregnancy and for children (to be used only for children over 10 years old because of the (Helichrysum italicum).
There are many suppliers who carry arnica infused oil, or, you can also easily make your own Arnica montana infused oil.
STEP 1- Dry the flower heads, herbs or plant material for a day or two.
Method- Dry plants by putting them in a basket with a cloth or paper towel in the bottom to soak up any moisture, hang them up, or place them in a paper bag.
STEP 2- Once the plant material is dry, you can chop, crush, or grind into small pieces or powder. You can infuse just one type of plant or a combination of plants like arnica (Arnica montana), rosehip (Rosa rubiginosa / Rosa canina) and calendula (Calendula officinalis).
STEP 3- Place 1 cup of arnica flowers into a pint glass jar and cover with 1-½ cups of olive oil. Fill the jar as far to the top as possible to prevent the infusion from going rancid or molding during the process.
Add a label to the jar with the ingredients and date of infusion.
Both olive and jojoba oils have a very long shelf life and will not easily go rancid. Olive oil is generally used for infusions of non-aromatic plants.
Jojoba oil would be a better choice for delicate aromatic flowers like rose (Rosa damascena), chamomile (Matricaria recutita) or lavender (Lavandula angustifolia).
STEP 4- This mixture is then left in a dark and warm environment for two to four weeks. If the room temperature is warmer it will infuse quicker.
Shake the mixture daily 25-40 times, until the base oil has absorbed the properties and essential nutrients from the plant material. When you see the plant material start to degrade it is time for the next step.
STEP 5- Drain off and filter the plant matter, using a funnel and strainer. You can also use an additional paper filter if there are any small particles of plant matter.
STEP 6- Bottle and label. It is always best to store the finished product in a dark amber bottle. You can also refrigerate it to extend the shelf life.
The end result is a wonderful carrier oil to use for your essential oil blends and products!
Precautions for External Application of Infused Oil: Do NOT use on wounds or internally: Don't apply arnica oil to damaged or broken skin. “Arnica oil contains a compound called helenalin, which may cause allergic reactions in people with sensitivity. If you develop a mild rash while using arnica oil, you are probably helenalin-sensitive and should stop using the oil”. 
Allergy to ragweed and related plants: Arnica may cause an allergic reaction in people who are sensitive to the Asteraceae/Compositae family. Members of this family include ragweed, chrysanthemums, marigolds, daisies, and many others. If you have allergies, be sure to check with your healthcare provider before applying it to your skin. Do not take arnica by mouth. Pure arnica oil can be toxic if it gets inside the body, so avoid ingesting it.
If taken orally, this herbal oil may cause:
Heart irregularities and increased heart rate
Dizziness, tremors weakness and vomiting
Mucous membrane and gastrointestinal irritation 
Internal Precautions for Homeopathic Tablets or Pills: Digestion problems: Arnica can irritate the digestive system. Don't take arnica homeopathic tablets internally if you have irritable bowel syndrome (IBS), ulcers, Crohn's disease, or other stomach or intestinal conditions. Arnica montana contains the toxin helenalin, which can be poisonous if large amounts of the plant are eaten. Consumption of Arnica montana can produce severe gastroenteritis, internal bleeding of the digestive tract, nervousness, accelerated heart rate, muscular weakness, and death if enough is ingested.
Fast heart rate: Arnica might increase your heart rate. Don't take arnica if you have a fast heart rate. High blood pressure: Arnica might increase blood pressure. Don't take arnica if you have high blood pressure. Pregnancy and breast-feeding: Don't take arnica by mouth or apply to the skin if you are pregnant or breast-feeding. It is considered LIKELY UNSAFE. Surgery: Arnica might cause extra bleeding during and after surgery. Stop using it at least two weeks before a scheduled surgery.(1)
Resources used: (1) https://www.drweil.com/vitamins-supplements-herbs/herbs/arnica/ (2) http://articles.mercola.com/herbal-oils/arnica-oil.aspx Dechen, Shanti, Clinical Aromatherapy Level 1 Text, Crestone, CO 2017, p.61, 68, 103.