What is it?
A natural sediment from the beds of lakes, rivers and other inland waters, made of fine mineral particles that are coarser than clay but finer than sand. In cosmetics it is used in mud masks and other mud-based skin, body and hair products, where it absorbs oil and gives a tightening feel. Its mineral makeup depends on where it was collected.
Key information
- We found no published safety review of silt as a cosmetic ingredient.
- The EU lists silt as a cosmetic ingredient with no restrictions.
- Like natural clays, natural muds can contain heavy metals such as lead and cadmium, so supplier testing matters.
More information
The European Union's cosmetic ingredient database, CosIng, describes silt as a sediment from inland bodies of water and lists its functions as absorbent, astringent and humectant, with no restrictions and no safety committee opinion. We found no safety assessment of silt by the Cosmetic Ingredient Review (CIR), the EU's Scientific Committee on Consumer Safety or any other agency, and no published skin irritation or allergy studies.
The closest reviewed ingredients are natural clays. In 2023 the CIR Expert Panel concluded that naturally sourced clays such as bentonite are safe in cosmetics, except that the data were insufficient for products that may be inhaled, partly because some clays may contain crystalline silica, a human carcinogen, as an impurity. The Panel found that heavy metals in clays did not penetrate the skin and asked manufacturers to keep them low.
Heavy metals are the main quality issue with natural muds. A 2025 study of 95 samples of raw Dead Sea mud and mud-based cosmetics found generally low to moderate metal levels, but lead and cadmium occasionally exceeded the stricter “technically avoidable” benchmarks. The FDA recommends no more than 10 parts per million of lead in cosmetics applied to the skin and reports that over 99 percent of such products on the U.S. market are below that level.
Reality check: we found no evidence that silt in a mud mask causes harm, but it has never had a formal safety review and its composition varies by source. Avoid breathing dry mud powder. See also our profile for green clay.
Sources: European Commission CosIng: Silt; Cosmetic Ingredient Review: Amended safety assessment of naturally-sourced clays as used in cosmetics (2023); Biological Trace Element Research (2025): Analysis of heavy metal concentrations in cosmetics derived from Dead Sea mud and comparative products; FDA: Lead in cosmetics