Topical sodium thiosulfate is a compounded, prescription cream, gel, or solution. Sodium thiosulfate itself is a simple sulfur-containing salt that has been used in medicine for over a century, most familiarly as an intravenous antidote. Applied to the skin, it is used mainly for calcium deposits in the skin and, historically, for the fungal rash tinea versicolor.
Bayview prepares it at the concentration and in the base your prescriber orders — commonly 20% or 25%, sometimes combined with zinc oxide, and available as a jar, a metered pump, a solution, or a fragrance-free cream. Only a licensed prescriber can decide whether it is right for you.
How does it work?
Sodium thiosulfate appears to work in two quite different ways, depending on what it is being used for.
On calcium deposits. Sodium thiosulfate increases the solubility of calcium salts — the idea is that it converts poorly soluble calcium deposits into a more soluble calcium thiosulfate that the body can clear (StatPearls, Calcinosis Cutis). It also has antioxidant and blood-vessel-dilating effects. Honest caveat: the mechanism is not settled. Newer work suggests sodium thiosulfate may reduce soft-tissue calcification through pathways that have nothing to do with calcium binding (StatPearls, Calciphylaxis).
On fungus. On contact with the skin, sodium thiosulfate slowly releases sulfur and sulfurous acid. That gives it activity against Malassezia furfur, the yeast responsible for tinea versicolor, along with a mild keratolytic effect that helps shed the scaly surface layer (AHFS monograph). This is also the source of the sulfur smell.
What is it used for?
All topical uses are off-label. Here is what the literature actually supports, stated plainly.
Calcinosis cutis — hard calcium deposits in the skin, often seen with autoimmune connective tissue diseases such as dermatomyositis and systemic sclerosis. This is the most common reason topical sodium thiosulfate is prescribed today. A published case series and systematic review, plus a Mayo Clinic case series, report improvement in a substantial proportion of treated lesions, and a recent review puts topical improvement rates in the range of roughly 68–78%, with small lesions responding best. But the evidence is low- to moderate-level observational data — case series and retrospective cohorts, not randomized trials (J Clin Med review). Expect a treatment worth trying, not a proven cure.
Tinea versicolor (pityriasis versicolor) — sodium thiosulfate has a long history here, typically as a 25% lotion or solution applied twice daily, and it appears in the US in fixed combination with salicylic acid (AHFS monograph). Be honest about where it sits: the supporting studies are old and small, and modern first-line treatment is topical azoles such as ketoconazole, selenium sulfide, or zinc pyrithione, with oral fluconazole for extensive or recurrent disease. A sodium thiosulfate/salicylic acid shampoo remains among the listed options (Merck Manual). One thing to expect either way: the pale patches left behind take months to years to repigment after the yeast is gone.
Calciphylaxis — a serious condition, mostly in people with advanced kidney disease, in which calcium builds up in small blood vessels and causes painful skin ulcers. Intravenous sodium thiosulfate is routinely used off-label for it, and case series report improvement or resolution of skin lesions in more than 70% of patients — but no prospective trials have assessed it, and the evidence base is case reports, case series, and retrospective analyses (StatPearls, Calciphylaxis). Topical sodium thiosulfate is sometimes prescribed alongside systemic care as a wound-directed measure. Topical sodium thiosulfate is not a treatment for calciphylaxis and should not be relied on as one; calciphylaxis is managed by a specialist team.
Extravasation antidote — this is the best-established use, but it is a hospital procedure rather than a home therapy. Sodium thiosulfate is a recognized antidote when the chemotherapy drug mechlorethamine leaks out of a vein into surrounding tissue: the manufacturer's labeling directs prompt infiltration of the area with sterile isotonic (1/6 molar) sodium thiosulfate plus an ice compress, and a 2% solution for accidental skin contact (Mustargen label). It also appears in some institutional protocols for cisplatin extravasation.
Bayview Pharmacy does not provide consultations or determine whether a formulation is appropriate for you; that is your prescriber's decision, and a valid prescription is required.
How do the strengths and forms compare?
The preparations differ mainly in concentration, in whether zinc oxide is included, and in how they are packaged. Zinc oxide adds a protective barrier and is often chosen for ulcerated or fragile skin. The table below is for education only.
| Preparation | Typical size | Notes |
|---|---|---|
| Sodium thiosulfate 20% cream (metered pump) | 50–60 mL | Pump delivers a measured 0.5 mL per actuation, which helps with consistent dosing |
| Sodium thiosulfate 25% cream | 60 mL | The most commonly dispensed strength |
| Sodium thiosulfate 25% cream, fragrance free | 60 mL | Chosen when fragrance is irritating or when masking is not wanted |
| Sodium thiosulfate 25% in zinc oxide cream (jar) | 60 g | Zinc oxide adds a barrier; often used over ulcerated deposits |
| Sodium thiosulfate 25% / zinc oxide 20% gel (jar) | 60 g | A thicker preparation that stays where it is placed |
| Sodium thiosulfate 25% solution | 30 mL or 175 mL | Used where a liquid is preferred, including larger areas |
| Custom | As ordered | Other concentrations, bases, and container types as your prescriber specifies |
Preparations are described for education only and are not a statement that any strength or base is better for a particular person. Your prescriber selects the concentration, the base, and the schedule. Bayview also compounds oral sodium thiosulfate capsules when a prescriber orders them; those are a separate preparation and are not covered by this page.
How is it used?
Use it exactly as your prescriber directs. Regimens vary by condition and by prescriber, but the pattern is usually a thin layer applied to the affected area once or twice daily. For calcinosis cutis it is typically applied over the calcium deposits and sometimes covered with a dressing; for tinea versicolor the historic regimen is a 25% lotion or solution twice daily to clean, dry skin.
Wash and dry the area first, apply only to the areas your prescriber specifies, and wash your hands afterward unless your hands are the treatment site. Patience matters: response is measured in weeks to months, not days, and stopping early is a common reason treatment appears to fail. Do not increase the amount, extend the area, or stop on your own — check with your prescriber first. A Bayview pharmacist is available if you have questions about your prescription.
Side effects & safety
Topical sodium thiosulfate is generally well tolerated when applied to a limited area. The effects people notice most are local: stinging or burning on application (more likely on broken or ulcerated skin), redness, itching, dryness, and peeling or flaking. If irritation is persistent or severe, contact your prescriber — the usual advice is to stop and reassess rather than push through.
Sodium thiosulfate absorbed through the skin is expected to be minimal, but the body-wide effects seen with high-dose intravenous use — nausea, vomiting, and disturbances of blood acid balance — are worth knowing about if you are applying it to large or ulcerated areas. Tell your prescriber if you develop nausea, vomiting, unusual fatigue, or shortness of breath during treatment. Get emergency care for signs of a serious allergic reaction such as widespread rash, swelling of the face or throat, or trouble breathing.
Who should not use it?
Do not use it if you are allergic to sodium thiosulfate or to any other ingredient in your preparation, including zinc oxide or the base, if those are part of your formula.
Use caution and talk to your prescriber first if you have kidney disease (sodium thiosulfate is cleared by the kidneys, and systemic exposure is higher when kidney function is reduced), if you would be applying it over large areas or over open ulcers, or if you are pregnant, may be pregnant, or are breastfeeding — topical sodium thiosulfate has not been studied in pregnancy. Do not use it on children unless a prescriber specifically directs it. Give your prescriber your full health history, your allergies, and a complete list of your medications so they can decide whether it is appropriate for you.
How should it be stored?
Store exactly as directed on your label. Compounded sodium thiosulfate creams, gels, and solutions are generally kept at controlled room temperature, roughly 68–77°F (20–25°C), with brief excursions permitted between 59–86°F (15–30°C), away from heat and direct light. Some formulations are labeled for refrigeration — follow your label rather than a general rule.
Keep the container tightly closed, since exposure to air can degrade the product and worsen the odor. Sodium thiosulfate solutions can form crystals or turn cloudy over time; if your preparation changes in appearance, separates, or develops an unusual odor beyond the normal sulfur smell, contact the pharmacy before using it. Do not use it after its beyond-use date, keep it out of the reach of children, do not share it, and dispose of unused medication as directed by your pharmacist.
Why is this compounded?
There is no FDA-approved topical sodium thiosulfate product in the United States. The FDA-approved sodium thiosulfate products are injections — the cyanide antidote given with sodium nitrite, and Pedmark for reducing cisplatin-related hearing loss in children — and neither can be applied to the skin. Prescribers who want a topical preparation have no commercial option.
Compounding lets the prescriber set the concentration (commonly 20% or 25%), decide whether to include zinc oxide, choose a cream, gel, or solution, select a fragrance-free base when odor or sensitivity is an issue, and pick a container — jar, metered pump, or bottle — that fits how and where the medication will be used. As a 503A compounding pharmacy, Bayview Pharmacy prepares each order in small batches using quality ingredients. Compounded preparations are not FDA-approved, and a valid prescription is required.
Clinical details for prescribers
Regulatory status. Sodium thiosulfate is not a controlled substance. No topical sodium thiosulfate product is FDA-approved in the US. Approved parenteral products: sodium thiosulfate injection (sequential use with sodium nitrite for acute cyanide poisoning) and PEDMARK (sodium thiosulfate injection, approved 2022, to reduce the risk of ototoxicity associated with cisplatin in pediatric patients ≥1 month with localized, non-metastatic solid tumors). All topical use is off-label and requires compounding. Compounded preparations are not FDA-approved.
Formulation & SIG. Compounded topical sodium thiosulfate 20% and 25%, ± zinc oxide 20%, as cream, gel, or solution; jar, metered pump (0.5 mL/actuation), or bottle; fragrance-free bases available. Common sizes 50–60 mL / 60 g, with 30 mL and 175 mL solutions. Typical SIG: apply a thin layer to the affected area once or twice daily, ± occlusion. Oral sodium thiosulfate 300 mg capsules are also compounded on order.
Evidence & clinical points:
- Calcinosis cutis: case series and systematic review support topical 10–25% STS; reported improvement roughly 68–78%, best for small/superficial lesions; intralesional preferred for larger lesions. Evidence is low- to moderate-level observational, predominantly in connective tissue disease–associated disease
- Calciphylaxis: IV STS is routine off-label practice with >70% lesion improvement in case series, but no prospective trials; topical STS is adjunctive wound care, not a treatment for the underlying process
- Tinea versicolor: historic 25% lotion/solution BID; evidence is old and limited; topical azoles, selenium sulfide, and zinc pyrithione are first-line, with oral fluconazole for extensive/recurrent disease. Counsel that hypopigmentation persists months to years post-clearance
- Extravasation: mechlorethamine labeling directs infiltration with sterile isotonic (1/6 M) sodium thiosulfate plus ice compress; 2% solution for accidental skin contact. Also used in some cisplatin extravasation protocols
- Caution with renal impairment and with application over large or ulcerated surfaces (systemic exposure, GI upset, metabolic acidosis with high systemic doses)
- Counsel patients on the characteristic sulfur odor up front; it is the leading reason for discontinuation. Fragrance-free and alternative bases are available
Ordering: e-prescribe to Bayview Pharmacy, or fax 401-284-4506. Background: StatPearls, Calcinosis Cutis; StatPearls, Calciphylaxis.
This is a prescription compounded medication and is not FDA-approved. This information is educational and is not medical advice. Bayview Pharmacy does not provide consultations or determine whether a formulation is appropriate for you — your prescriber decides that and sets the concentration, the base, and the schedule.
