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7
Subchronic Toxicity

The subchronic rat inhalation NOEL of 200 mg/m
3
(0.2 mg/I) was determined from a single concentration
study. Extensive monitoring of human patients have shown that DMSO does not affect human renal function.
DMSO is a diuretic but no sign of kidney damage has been found in humans or laboratory animals after repeated
DMSO treatment. Hemolysis has been reported in animals that received DMSO intravenously.

Skin Exposure
DMSO easily penetrates the skin (176 ± 42 g/m
2
/hr) compared to, for example, water (14.8 ± 0.1 g/m
2
/hr),
but because of DMSO's low toxicity (see previous section) and the fact that this same permeability test
showed DMSO does not carry less-permeable substances with it through the skin, it can be concluded that
DMSO does not pose a significant threat by skin absorption. The penetration rate of DMSO in solutions is a
direct function of the mole fraction of DMSO. (Ursin, et. al. 1995)
14
. Although DMSO readily penetrates human
skin in concentrations of 70-100%, at concentrations of 67% or less, DMSO molecules are hydrated, which
greatly reduces dermal penetration (Sulzberger et. al., 1966; Brayton, 1986: Woodford and Barry, 1986).

No significant abnormalities were found in extensive physical examinations or analyses of blood and urine
during repeated applications of large amounts of DMSO to the skin of humans over a long period of time.
This was reported by Dr. Richard Brobyn
(2)
to the New York Academy of Sciences. DMSO was used in two
human studies lasting 14 and 90 days. In each case, one gram of DMSO per kilogram of body weight was
applied each day by each subject to his own skin. In an (80 kg = 176 lb) individual, it was 80 grams or 2.7 fl.
oz. This amount required up to 2 hours for complete absorption from the 90% DMSO gel.

No frank evidence of intolerance resulted from dermal application of 9 grams/kilogram of 90% DMSO to
Rhesus monkeys daily for 18 months. In a small (50 kg = 110 lb.) individual, this would amount to daily appli-
cations of 15.2 fluid ounces or nearly a pint of 90% DMSO.

Observation has indicated that skin application, particularly if frequent with large amounts of DMSO, may
result in reddening, itching and burning at the application site. Exposure to large amounts of DMSO by skin
or elsewhere may result in sedation, headache, nausea or dizziness.

Chronic Toxicity

DMSO is not listed as a carcinogen by regulatory agencies such as IARC, NTP, OSHA or ACGIH, based on
reviews of numerous studies. An 18-month study with rhesus monkeys established an oral NOEL of 3300
mg/kg/day. No tumors were observed and bone marrow smears from the monkeys that received oral or topi-
cal doses of DMSO at up to 9 g/kg/day.
12
This is comparable to an average human (70 kg or 154 lbs) con-
suming approximately 210 g (or nearly 1/2 pound) DMSO per day, i.e., 3g/kg/day
.
In fact, 84 humans that
have received daily topical treatment of 2.8 g DMSO/kg/day (equivalent to nearly 1/2 pound/day/person) for
up to three months showed no DMSO-related effects beyond occasional skin irritation, garlicky breath and
body odor. Additionally, (Hull et al. 1969)
(7)
found no DMSO-related effects in any of the 38 humans, age 21-55,
who received a topical application of an 80% DMSO gel in a single daily dose of 1 g/kg for 12 weeks.