Calomel is also known as mercurous chloride or Mercury(I) chloride. In China it is called Qing Fen, which was an important ingredient in ancient alchemy to make pills and a Chinese herb that is frequently used for the treatment of psoriasis and genital warts in folk medicine. More than that, medicinally it is also used alone or combined with other herbs to treat a variety of diseases, including swelling and ulcer, itchy scabies, eczema, acne rosacea, syphilis, chancre, body odor, tinea versicolor, penile cancer, early cervical cancer, fistula, chronic dacryocystitis, neurodermatitis, asthma, and so on. Although calomel has many great natural properties to make it perfect for medicinal uses, it comes with many side effects since it may lead to mercury poisoning. Therefore, you have to be aware and know about these effects before using it, externally or internally.
What is calomel?
Medicinally it refers to the crystalline powder (Hg2Cl2) made from mercury, alum (or blue vitriol), salt and others by crystallization or sublimation. In China it is mainly produced in Hubei, Hunan , Shanxi, Shaanxi, and Guizhou. And it should be protected from light and used ground finely.
Calomel is white, silvery, and usually in the shape of snowflakes. It is light and easy to be twisted into white delicate powder by hand. In terms of medicinal quality, the preferred one is white, in bigger pieces, bring, in needle-like crystals, light, and with no silver beads. It is insoluble in water and acid. If heated on iron, it gradually becomes yellow, turns into smoke, and finally leaves no trace. If blended with potassium hydroxide solution, it dissolves out black mercurous oxide; if added in ammonia and the shaded, it becomes black.
It mainly contains mercurous chloride. As a mineral form, calomel is rarely found in nature. As a result, most of them now are made by man. It is odorless, colorless or usually with pale yellow, and scaly crystals. Chemically known as mercurous chloride, the content of HgCl in its dried product should not less than 99.6%. Low in toxicity as it is, if boiled with water it breaks up into mercuric chloride and metallic mercury, which are highly poisonous. And the exposure to light can also gradually darken the color of mercurous chloride and change its chemical property, which thus make it highly toxic.
What is calomel used for?
In the Western countries, calomel was a popular medicine for stimulating evacuation of the bowels, teething with babies, and killing bacteria in the nineteenth century. And in China it has a much longer history as a healing herb. As a matter of fact, minerals have long been an integral part of traditional Chinese medicine. Wu Shi Er Bing Fang (Recipes for Fifty-Two Ailments), the earliest Chinese medical text unearthed in the famous Mawangdui Han Tombs in the eastern suburb of Changsha City, recorded 21 kinds of mineral drugs. And Shen Nong Ben Cao Jing (Divine Farmer’s Materia Medica, the first book on herbology in the world, documented 46 kinds of mineral drugs and classified them into top, medium and low-grade drugs. These records include mercury, calomel, cinnabar, arsenolite, realgar, and more.
Calomel-based preparations are traditionally used for scabies, syphilis, acne rosacea, neurodermatitis, and asthma. And the results were quite satisfactory, according to the report. What’s more, in recent years it was also used for some other diseases.
(1). More than 100 cases of body odor were treated with topical Hu Chou San (body odor powder), which consists of the same amount of calomel and Hua Shi Fen (talcum powder). And the result was good.
(2). 31 cases of tinea versicolor were ever treated with topical Han Ban San (tinea versicolor powder), which is composed of equal amount of calomel and Hai Piao Xiao (Cuttlefish Bone). And the result was satisfactory.
(3). Penile cancer was treated with the pills made of Hong Fen (Hydrargyri Oxydum Rubrum) 9g, calomel 6g, mercury 3g, and appropriate amount of red jujube fruit. The pills are as big as mung bean. The remedy is 10 pills a time and no more than 2 times a day.
Modern pharmacological actions of mercurous chloride
1. It has broad spectrum antimicrobial activity. And it has good antibacterial effect on a variety of Gram-positive and -negative bacteria and pathogenic skin fungi;
2. Orally it has certain oral laxative and diuretic effect.
Sample mercurous chloride formulas on herbal remedies
Zhong Hua Ben Cao (Encyclopedia of Chinese Materia Medica) believes that it is acrid in flavor and cold and toxic in nature. It goes to meridians of liver, kidney, lung and large intestine. Major functions are killing parasites, counteracting toxic substances, removing dead and/or rotten tissue, relieving itching, eliminating phlegm, diuresis or purgation, and relaxing the bowels. And common calomel uses and indications include boils and ulcer, scabies, prurigo, scrofula, syphilis, malnutrition sores, rosacea, acne, acute and chronic infantile convulsions, asthma due to accumulation of phlegm in the lung, edema, and difficulty passing stool and urine. Recommended calomel dosage is from 0.1 to 0.2g in pills or powder internally.
1. Ge Fen San from Wai Ke Zheng Zong (Orthodox Exogenous Illnesses). It is combined with Huang Bai (Amur Cork Tree Bark), Ge Fen (mactra clam shell powder), Duan Shi Gao (calcined Gypsum), and cool or sesame oil to treat itchy, painful impetigo.
2. Ru Sheng San from Sheng Ji Zong Lu (Complete Record of Holy Benevolence). It is formulate with Feng Hua Shi Hui (weathered limestone), Qian Dan (Minium), and Liu Huang (Sulphur powder) to cure wet and oozing ringworm.
3. Jia Wei Dian Dao San from Chuang Yang Wai Yong Ben Cao (Materia Medica for Skin and External Diseases). It is equipped with Da Huang (Rhubarb) and Sulphur to treat rosacea and acne.
4. Zhou Che Wan from Dan Xi Xin Fa (Dan Xi’s Experiential Methods). It is matched with Rhubarb, Gan Sui (Euphorbia Kansui), Jing Da Ji (Euphorbia pekinensis), etc. to heal excess type edema and constipation.
5. Qing Fen Ding from Chuan Ya Nei Bian (Internal Treatise on Folk Medicine). It is coupled with egg white to treat dyspnea in children accompanied with excessive sputum.
Calomel side effects and contraindications
Calomel, or mercurous chloride, is the processed product extracted from mercury. It contains mercuric oxide. As everyone knows the inorganic mercury, in the forms of mercuric or mercurous, is poisonous. When mercury ions enter into human body, it will bond with the mercapto of enzyme protein and thereby inhibit the enzyme activity and impede normal cell metabolism. Topical use of high concentrations of mercury can directly damage the central nervous system and thus cause poisoning. And the poisoning symptoms include headache, nausea, drooling, numbness, swollen gums, insomnia, dreams, hallucinations, limb tremors, etc. Even worse, in severe cases it may lead to uremia, blood pressure lowering, heart failure, coma, rising urinary mercury, etc.
As the old saying goes, “all medicines are somewhat toxic.” For Chinese medicine that contains heavy metal, the use of calomel, in particular in oral administration, should follow the doctor’s advice, strictly control the dose, reduce the topical area as small as possible, and avoid long-term use. Once the poisoning symptoms occur, you should stop it immediately or hurry to go to hospital to get the care.
(1). Zhong Cheng Yao Yan Jiu (Research of Chinese Patent Medicine), 1980;7:45.
(2). Xin Zhong Yi (New Journal of Traditional Chinese Medicine), 1988;10:11.
(3). Zhong Yao De Miao Yong (Ingenious Use of Chinese Herbs), Pulished by Nanjing Publishing House, 1990:300.