What side effects or risks are reported with topical or oral DMSO?

The short version: topical DMSO has well-documented local side effects, oral DMSO has very little human safety data, and the evidence base is thin for both routes.

The most common side effect from topical DMSO is skin irritation. In a pooled analysis of seven trials on a 45.5% DMSO solution for osteoarthritis, 33% of patients reported dry skin compared to 5% on placebo [6]. Dyspepsia (upset stomach) occurred in 7.7% versus 2.9% [6]. About 12.7% of patients stopped the study because of side effects, versus 9.1% on placebo [6]. These are real numbers from real trials, but the trials were funded by the manufacturer of the product.

The garlic-like breath odor (halitosis) is the most famous DMSO side effect. In a 1965 study using 90% DMSO, five of six inpatients and nine of ten outpatients reported it [3]. In a 2009 study using a 45.5% solution made with high-purity DMSO (over 99.99%), only 12 of 1,243 patients reported it [3]. The 2024 review argues that higher purity reduces the odor, but no head-to-head purity comparison was ever done [3]. The claim is plausible but unproven.

A case report from 2002 describes a 19-year-old leukemia patient who received 99% topical DMSO for a chemotherapy extravasation and developed burning, swelling, and inflammation at the site [1]. He died one month later from fungal infection, but the DMSO was not the cause of death [1]. The case shows that high-concentration DMSO on damaged skin can cause local toxicity.

For oral DMSO, the human safety data is almost nonexistent. The only human-relevant oral study in the evidence is from 1986 in mice, where oral DMSO extended life span in autoimmune disease models [4]. That tells you nothing about human side effects. A 2018 horse study showed that oral DMSO reaches peak blood levels in about 45 minutes and has about 47% bioavailability [5]. In rats, DMSO was used as a vehicle for pesticides with no apparent toxicity at the doses used [10]. That is not human safety data.

The 2025 review of DMSO in stem cell products claims no significant safety concerns from intravenous DMSO at doses up to 132 mg/kg per infusion [2]. But that review covers intravenous and topical use in cell therapy, not oral DMSO, and it was written by researchers with ties to the cell therapy industry.

My call: topical DMSO causes predictable local skin irritation and breath odor, with severity depending on concentration and purity. Oral DMSO has no adequate human safety data to judge. Confidence: moderate for topical, low for oral.