Sulfur (sulphur) soap is a special-purpose soap for specific skin issues. It is not a soap for general bathing. Commercial makers make sulfur soap by milling sulfur powder into cool, low-moisture soap using specialized equipment.
Most handcrafted soap makers must use other ways to incorporate sulfur into soap. The information I present here is based on advice generously shared by long-time sulfur soapers as well as on my limited personal experience.
Is sulfur soap effective as a medicinal product?
In discussing sulfur soap with other people, I have learned that people use this soap for skin conditions such as acne, rosacea, dermatitis, dandruff, and fungal infections. Some people use sulfur soap to repel chiggers and control skin parasites such as scabies, demodex mites, and lice. A few people say they use sulfur soap to treat poison ivy rash or mite and chigger bites.
The US Food and Drug Administration (FDA) has approved sulfur for treatment of acne in concentrations from 3% to 10%. (1, 2) I have not researched if sulfur soap is approved by the FDA for the other skin issues listed above. You will need to do your own research to determine the efficacy and safety of sulfur soap for the purpose you have in mind.
Can sulfur soap be sold as a medicinal product?
Yes, you may be able to do this, but do so responsibly and legally.
In the US, you cannot legally make drug or medicinal claims about any product unless you can first document its effectiveness. If the product is effective, you must then meet labeling and registration requirements and comply with restrictions for selling a medicinal product. Get started on this process by reading the FDA's Frequently Asked Questions on Soap.
Some soapers choose to ignore the law and make unfounded medical claims about their products. They will share customer testimonials about the benefits of the product or explain how the product was used in the past for treating certain problems. The FDA takes a dim view of "weasel words" and unfounded claims like this. Drug claims are still drug claims, no matter how indirect a seller is when making these claims.
Safety cautions about working with sulfur
If you make sulfur soap, you will be exposed to sulfur powder, hydrogen sulfide gas, and possibly sodium sulfates, sulfur oxides, and/or sulfuric acid. Use very good air ventilation or work outdoors when making sulfur soap.
Do not inhale sulfur powder. It is irritating to the eyes, nose, throat, and lungs. Wear a particulate respirator and use very good ventilation when handling the powder.
Avoid getting sulfur powder on your skin. It can be drying and irritating. Wear gloves and protective clothing when working with sulfur powder.
Sulfur combined with water or lye solution will create hydrogen sulfide gas (H2S gas with a rotten egg odor) especially at higher temperatures. Hydrogen sulfide gas is toxic, not just stinky. Your nose quickly becomes used to hydrogen sulfide, so you cannot use your sense of smell as a safety guide.
A respirator will not remove this gas, so use good ventilation to control your exposure to hydrogen sulfide gas. This also goes for any of the other sulfur-based chemicals that may also form when making this soap.
Choosing the right kind of sulfur
The sulfur to use in soap should have a purity of 99% or higher.
Sulfur with less than 99% may contain other ingredients not suitable for use on skin. For example, "flowable" sulfur powder includes additives so the powder mixes easier with water.
Use only a powdered form of sulfur. Sulfur flakes and crystals are too abrasive to use on skin.
Sulfur powder has many names including --
Sublimed sulfur (aka flowers of sulfur)
Precipitated sulfur (aka milk of sulfur)
Lime sulfur (sulfur boiled with lime)
Washed sulfur (sulfur treated with aqueous ammonia) (5)
Colloidal sulfur (very fine powder)
Micronized sulfur (very fine powder)
You may want to sift sulfur powder to remove coarse particles before adding it to soap.
If the sulfur powder has large hard clumps or shows other signs of degradation, avoid using it in soap.
Use an appropriate soap recipe
Stick with basic, familiar, reliable recipes and methods for the best chance of success.
Design a recipe with a low to moderate superfat (2% to 5%) and a low to moderate amount of coconut oil (perhaps 10% to 25%). The soap should be an effective cleanser without being overly drying and irritating.
Do not use untested additives such as milk, sugars, fragrances, salts, oatmeal, high superfat, etc. They may react unexpectedly with the sulfur.
Lanolin can be used in sulfur soap. (3) If you want to include lanolin in your recipe, I suggest 2% to 5% based on total fat weight.
See the next two sections below for the recommended maximum amounts of sulfur to use. These limits are based on advice from soap makers experienced with making sulfur soap. You will have the best chance of success if you do not exceed their recommendations.
Cold process (CP) tips
For the best chance of success with a CP method, keep the sulfur at or below 1% by weight based on the total weight of oils. This is approximately 1 teaspoon ppo.
One soap maker tested higher dosages and found 1 tsp ppo (about 1% based on total fat weight) gave her the most reliable results. She reported this dosage is effective for treating poison ivy rash, rosacea, and acne. (3)
Another soap maker shared he uses 1.5 to 2 tsp ppo (about 1.5 to 2% of total fat weight) with good results. (4)
These varying results might be caused by differences in the sulfur powder composition and/or differences in the soaping methods used by these soap makers.
At sulfur dosages higher than 2% of total fat weight, CP soap will almost certainly fail -- it will turn dark brown and stay permanently soft.
Soap cool! Use ingredients that are at or near room temperature. Use smaller individual molds or a slab (tray) mold to keep the soap as cool as possible during saponification. The soap is likely to get too hot in a cylinder or log (loaf) mold. Cool the soap in the mold by setting the mold on several cans or other supports and blowing air over the mold with a fan. Do not CPOP (warm the soap in the oven) or insulate the mold.
CAUTION: Do not put CP soap in the fridge or freezer to keep it cool. If you do, you may expose your food to sulfur soap, hydrogen sulfide, and other chemicals that should not be in food.
Sulfur powder does not dissolve in water or fats. The powder is difficult to mix into liquids of any kind, although it works best if mixed with fats. Add the powder to the fats and carefully mix with a spatula or spoon to get the powder wetted. Then stick blend or whisk to eliminate all lumps. Be sure to use good ventilation when working with sulfur powder.
The soap batter may take a long time to come to trace.
The saponifying soap may create hydrogen sulfide gas and other gases. Put the soap in a well ventilated place away from people and pets.
Hot process (HP) tips
Keep the sulfur at or below 10% of total fat weight. The most common sulfur dosages I found for HP sulfur soap were 3-4% ppo and 8-10% ppo.
Make the HP soap without sulfur using your normal HP method. Mix the sulfur powder into the soap only after the soap is fully cooked, tests zap free, and is as cool as possible.
Sulfur powder is a lot more difficult to mix into finished HP soap, compared with mixing it into the fats for CP soap.
Curing and using the soap
Cut and cure the soap as you normally do.
Objectionble odors will fade over time, but may not entirely disappear.
A "bloom" of fine sulfur powder may appear on the surface of the soap bars at times. It washes off easily when the bar is used.
For best results, apply soap lather to the affected skin and let the suds remain on the skin for several minutes before rinsing well.
Avoid getting the lather in eyes. Rinse well and get medical attention if this happens.
Some people's skin is sensitive to sulfur. If this soap causes irritation or redness, discontinue use.
References
(1) Title 21 -- Food and Drugs Chapter 1: Food and Drug Administration Department of Health and Human Services: Subchapter D -- Drugs for Human Use: Part 333 -- Topical Antimicrobial Drug Products for Over-the-Counter Human Use: Subpart D -- Topical Acne Drug Products: Section 333.310 Acne active ingredients. FDA. April 1, 2019. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=333.310
(2) Guidance for Industry: Topical Acne Products for Over-the-Counter Human Use... US Food and Drug Administration (FDA). June 2011. https://www.fda.gov/media/80442/download
(3) KYwoman. Private message on the now-defunct The Dish Forum. 2013. No public archives are available.
(4) PapaBearSpa on Etsy as quoted by RoseValleyGirl in Post #5 in "Sulfur Soap" thread. March 10, 2013. https://www.soapmakingforum.com/threads/sulfur-soap.32787/
(5) Muellers Lane Farm. Post #5 in "Sulfur soap" thread. December 13, 2014. https://www.homesteadingtoday.com/threads/sulfur-soap.529830/
Also see: Roberto Akira. "Sulfur soap -- A trial." April 30, 2013. http://www.japudo.com.br/2013/04/30/sulfur-soap-a-trial/
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