Sulfur: One of the Oldest Ingredients in Soap Chemistry

In Brief: Sulfur (INCI: Sulfur) is a natural element with a long history in soap and cosmetic chemistry. Sulfur's interaction with keratin is examined in the literature. In soap-making, sulfur is found in traditional cleansing recipes preferred for oily and combination skin.

Sulfur in soap is a traditional cleansing ingredient preferred for oily and combination skin. Sulfur, positioned as element 16 on the periodic table, is a yellow-colored, odorless (in pure crystalline form), brittle solid. Found in nature both as a free element and in compounds, sulfur has a history of at least 3,500 years in topical use, documented in the Ebers Papyrus (circa 1550 BCE), continuing to modern cosmetic recipes. The scope of this monograph is clear: soap is a cosmetic cleanser; the information below conveys sulfur's chemical and historical profile without making any medical or healing claims. This is a cosmetic ingredient monograph; not a product recommendation or medical advice.

This article is not a product promotion. Its purpose is to present an independent framework regarding sulfur's position in scientific literature. This is a cosmetic content monograph; not product or medical advice.

History: A Traditional Ingredient in Cosmetic Heritage

One of the earliest written records of sulfur's use in skincare is found in the Ebers Papyrus, dated to around 1550 BCE—one of the oldest known medical texts. Hippocrates (460-370 BCE) described sulfur in various topical preparations; Roman naturalist Pliny (23-79 CE) outlined topical uses of sulfur in Natural History; during the Middle Ages, Arab and Persian physicians (including Avicenna) used sulfur in skin preparations.

In the modern era, sulfur became a common topical ingredient from the 19th century onward. Its popularity declined in the mid-20th century but has seen renewed interest in recent years with the rise of "natural actives." Lin and Reimer's 1988 article "Sulfur Revisited" published in the Journal of the American Academy of Dermatology is a comprehensive review evaluating sulfur's historical and chemical position.

Physical and Chemical Properties

Elemental Sulfur

Sulfur (S, atomic number 16, atomic weight 32.06) is a yellow-colored, odorless (in pure crystalline form), brittle solid. In nature it is found both as a free element (in volcanic regions—the sulfur mines of Sicily, Italy, are historically significant) and as sulfate (CaSO₄, MgSO₄) and sulfide (FeS₂, ZnS) compounds. It exhibits allotropy, with its most stable form being the S₈ ring structure (orthorhombic sulfur).

Sulfur in Cosmetic Form

The primary forms of sulfur used in cosmetic recipes are:

Precipitated sulfur (milk of sulfur): Fine particle-sized, yellowish-white powder. The most common form used in topical formulations.
Colloidal sulfur: Sulfur in suspension as very fine particles. Provides homogeneous distribution.
Sublimed sulfur (flowers of sulfur): Fine powder obtained by vaporization and condensation. The traditional form.

Chemical Behavior of Sulfur (Literature)

Interaction with Keratin (Literature)

Sulfur's interaction with keratin—examined in the literature—weakens desmosomal bonds between corneocytes in the skin's outermost layer (stratum corneum). This mechanism, which supports the shedding of dead skin cells from the surface, is a well-documented chemical behavior. This chemical mechanism is explained through sulfur's reaction with the skin's cysteine amino acid, producing polysulfones and hydrogen sulfide (H₂S).

In Vitro Microbiology Studies

In in vitro studies on sulfur's metabolic transformation products (polysulfones, pentathionic acid), inhibitory activity has been reported against certain bacterial and fungal species. These findings are laboratory-based and do not constitute a product claim.

Interaction with Sebum

Sulfur's interaction with sebum (skin oil) is an area of research in the context of oily skin. Sulfur's interaction with keratin forms the chemical basis of these investigations.

Position in Scientific Literature

Sulfur has long been examined in dermatology and pharmacology literature; Gupta and Nicol's review (2004) and Lin and Reimer's "Sulfur Revisited" article (1988) are comprehensive evaluations of this literature. Medical and pharmaceutical uses mentioned in these studies—topical pharmaceutical preparations, combinations, and prescription formulations—belong to the human pharmaceutical product context and are outside the scope of this cosmetic content monograph. The purpose here is to convey sulfur's chemical behavior and historical continuity of use; no medical or healing claims are made.

Safety Profile and Notes

General Safety

In cosmetic ingredient safety assessments (e.g., CIR—Cosmetic Ingredient Review), sulfur at low concentrations is generally considered safe for cosmetic use. Its thousands of years of historical use provides context supporting its safety profile.

Possible Effects and Points of Attention

The most commonly reported effects are skin dryness, peeling, mild irritation, and temporary redness—these are expected outcomes of sulfur's chemical behavior. Formulation with moisturizing ingredients (glycerin, shea butter, aloe vera, and similar materials) helps reduce these effects. At higher concentrations (%5+), dryness and irritation are more likely.

Odor

The most notable characteristic of sulfur is its distinctive odor. Pure sulfur is actually odorless, but during its transformation on the skin, sulfur compounds may form an odor reminiscent of "rotten eggs." This odor is more pronounced at higher concentrations; in cosmetic formulations, it is commonly masked with essential oils.

Points of Caution

Though rare, sulfur allergy is possible. Sulfonamide (antibiotic) allergy is different from elemental sulfur allergy. Contact with open wounds and mucous membranes should be avoided; those with skin sensitivity or known skin conditions should consult a health professional.

Sulfur in Soap-Making

In soap, sulfur most often appears in traditional cleansing recipes aimed at oily and combination skin; the key factors determining the outcome are the correct sulfur form, usage rate, and application technique.

Time of Addition and Method

In cold-process soap making, sulfur is added at trace stage as a fine powder (precipitated or colloidal sulfur). To prevent clumping, pre-mixing (slurry) with a small amount of liquid oil is recommended. Sulfur undergoes certain chemical transformations in an alkaline environment—therefore, it is not accurate to say that all sulfur remains in its original form in the soap structure.

Usage Rate

In soap recipes, sulfur is typically used at 1-5% of the total oil amount. In practice, this means approximately 5-25 grams per 500 grams of oil (1-5 teaspoons). 3% is a common and balanced starting rate. Higher rates (%5+) noticeably affect the soap's odor and increase the likelihood of skin dryness.

Properties Sulfur Imparts to Soap

Sulfur imparts the following properties to soap:

Color: Yellowish-greenish tone. As the ratio increases, the color becomes more pronounced.
Odor: At lower rates (%1-3), odor is minimal; at higher rates (%5+), sulfur odor may be noticeable. Masking with essential oils is common.
Texture: May impart a slightly grainy texture—dependent on particle size (finely colloidal sulfur yields smoother results).

Combination with Juniper Tar: A Classic in Turkish Soap-Making

In Turkish soap-making tradition, the combination of sulfur and juniper tar in producing "juniper tar and sulfur soap" is a classic and highly popular recipe. This combination balances juniper tar's strong odor with sulfur's odor, bringing together the characteristic properties of both ingredients. According to Google Trends data, "sulfur soap," "juniper tar soap," and "juniper tar and sulfur soap" are high-search-volume terms in Turkey.

Frequently Asked Questions

What is sulfur?

Sulfur (S), positioned as element 16 on the periodic table, is a natural element. With at least 3,500 years of use in topical applications, it is one of the oldest ingredients in the cosmetic tradition.

How does sulfur work on the skin?

Two primary chemical behaviors of sulfur are documented: its interaction with keratin (a chemical behavior associated with surface cell renewal) and inhibitory activity reported in in vitro microbiology studies. These chemical behaviors are explained through polysulfones and hydrogen sulfide (H₂S) produced by sulfur's transformation on the skin (not constituting a cosmetic claim).

What does sulfur do in soap?

Added to soap recipes at 1-5%, it gives traditional "sulfur soap" its character. Its combined use with juniper tar (juniper tar and sulfur soap) is one of Turkish soap-making's classic recipes.

Is sulfur soap suitable for oily skin?

Sulfur is traditionally preferred in an oily and combination skin context. Since it can be drying, formulas balanced with moisturizing ingredients should be preferred; use 2-3 times per week rather than daily is a reasonable approach. Those with skin sensitivity should consult a health professional.

Is sulfur safe?

In cosmetic ingredient safety assessments (CIR), sulfur at low concentrations is generally considered safe for cosmetic use. The most commonly reported effects are skin dryness and mild irritation; formulations balanced with moisturizing ingredients reduce these.

Chailea Products Containing This Ingredient

Natural Juniper Tar and Sulfur Soap 100 g
Natural Sulfur Soap 100 g

References

Gupta AK, Nicol K. The use of sulfur in dermatology. Journal of Drugs in Dermatology, 2004; 3(4):427-431. PubMed.
Lin AN, Reimer RJ. Sulfur revisited. Journal of the American Academy of Dermatology, 1988; 18(3):553-558. PMID: 2450900. PubMed.
CIR — Safety Assessment of Sulfur in cosmetics. Cosmetic Ingredient Review.

Chaileapedia is an educational reference about cosmetic ingredients and the science of soapmaking. It is not intended to diagnose, treat, cure or prevent any disease.