Zinc Sulfate

What it is

Zinc sulfate is the inorganic zinc salt of sulfuric acid, which the Cosmetic Ingredient Review records as soluble in both its mono- and heptahydrate forms and lists for use as a cosmetic astringent, cosmetic biocide and oral care agent. It is one of two zinc salts on the masks here whose status the regulation does not leave to be worked out, the other being zinc gluconate. The consolidated Annex III names it in the Common Ingredients Glossary column by name, spelled the British way as Zinc Sulphate, and carries the CAS numbers that identify the same substance our corpus prints as Zinc Sulfate. That spelling is the only reason a reader might expect the two to be different substances; they are not. What is particular to this salt is how recently that became true. The entry was rewritten in 2026, and the Cosmetic Ingredient Review's 2018 account of it listed four zinc salts - zinc acetate, zinc chloride, zinc gluconate and zinc glutamate - with this one not among them. The rewrite added two names, zinc citrate and zinc sulphate, and of those two only zinc sulphate appears on a mask here. So the stale four-name account is stale for this salt in particular, and not for zinc gluconate, which was named all along.

How it shows up on a label

What it does well

• Reviewed by the expert panel and found safe as used

  Zinc sulfate was one of the 27 zinc salts the Cosmetic Ingredient Review Expert Panel assessed together, and the Panel concluded that all 27 are safe in cosmetics in the present practices of use and concentration described in that assessment, when formulated to be non-irritating. That is a conclusion about the salt as it is actually used rather than a finding that it does anything in particular to skin.

  Moderate evidence

Worth knowing

• The 1% cap is about swallowing, not about skin

  The limit on water-soluble zinc salts exists because zinc from oral-care products is swallowed, rather than because of a skin hazard the regulators identified - which is a point about why the cap exists, not a claim that the salt is inert on skin. The Cosmetic Ingredient Review reports the committee reasoning behind it: exposure estimates for water-soluble zinc salts in toothpastes at 1% and mouthwashes at 0.1% could give daily intakes of 3.54 mg for adults and for children aged 6 to 17, which is up to 14% of the 25 mg per day upper limit for adults. A face mask is caught by the same entry, but not by that reasoning.

  Matters most toNobody reading it as a skin warning; it is a formulation limit. The irritation record below is a separate question.

• Severely irritating to the eye as a neat material

  This is the harshest result in the Cosmetic Ingredient Review's eye testing of the zinc salts, and it belongs on the page. Roughly 98.1 mg of undiluted zinc sulfate - 39.7 mg as zinc - was instilled into the eye of three rabbits under OECD Test Guideline 405 and left unrinsed. The report grades it severely irritating: corneal injury in two of the three reversed within 24 to 72 hours, redness, swelling and discharge of the conjunctiva appeared in all of them, and from day 7 to the end of the study the eyelid tissue, nictitating membrane or sclera carried yellow-white spots the study authors read as a sign of necrosis. The summary sentence places it at the bottom of the range: in rabbit eyes zinc phosphate and zinc ricinoleate were non-irritating, zinc nitrate irritating, zinc lactate very irritating, and zinc sulfate severely irritating. What that test is not is a mask on a cheek - it is neat powder held against an eye for days. Read it as a reason to keep the product out of the eye rather than as a verdict on the mask.

  Matters most toAnyone laying a sheet mask close to the eye area, or rinsing a wash-off mask near the eyes; contact-lens wearers in particular.

• Mildly irritating to skin at the concentration the cap allows

  The same report tests the salt on skin as well, and the result is mild but not nothing. At 1% in deionised water - which is the maximum a face mask may carry as zinc - a five-day open patch test found it slightly irritating in mouse, rabbit and guinea pig alike, and a closed rabbit patch test over three days then two found the same. Against that, a four-hour semi-occlusive patch of the undiluted material was non-irritating to rabbit skin, and a 10% solution was non-sensitising in a mouse local lymph node assay, so this is irritation with repeated contact rather than sensitisation. The Panel's conclusion covers the salt when formulated to be non-irritating, which is the condition doing the work here.

  Matters most toPeople with sensitive skin, and anyone leaving a mask on for longer than the instructions give.

Where the EU stands

Sources (2)

Every link goes to the original: a journal, a PubMed record or an EU document.

1. [1]
   Safety Assessment of Zinc Salts as Used in Cosmetics

   Cosmetic Ingredient Review Expert Panel, Final Report · 2018

   Zinc Sulfate is one of the 27 inorganic and organometallic zinc salts assessed together, concluded "safe in cosmetics in the present practices of use and concentration described in this safety assessment when formulated to be non-irritating". The report records it as the inorganic salt, CAS 7446-19-7 (monohydrate) and 7446-20-0 (heptahydrate), functioning as a cosmetic astringent, cosmetic biocide and oral care agent, with water solubility "Soluble (mono- and heptahydrate)" and an estimated log P of -0.07 - note that "Freely soluble" is the descriptor the same table reserves for Zinc Gluconate. The report's irritation record is mixed and is carried into the concerns above: on skin, "Zinc Sulfate (1% in deionized water) was slightly irritating in all three species" in a five-day open patch test and slightly irritating in a closed rabbit patch test, while a four-hour semi-occlusive patch of the undiluted material was non-irritating to rabbit skin and a 10% solution was non-sensitising in a mouse local lymph node assay. In the eye it is the worst of the salts tested: "Zinc Sulfate (undiluted) was severely irritating", from ~98.1 mg instilled into three rabbits' eyes under OECD TG 405 and left unrinsed, with corneal injury in two animals reversed by 24 to 72 h, conjunctival redness, chemosis and discharge in all, and yellow/white spots on eyelid tissue, nictitating membrane and/or sclera from day 7 through study termination that the study authors considered indicative of necrosis. Checked 5 October 2026.

2. [2]
   Regulation (EC) No 1223/2009 on cosmetic products, consolidated text 02009R1223 - EN - 18.05.2026 - 041.001

   EUR-Lex, Official Journal of the European Union · 2026

   Annex III entry 24, as amended, heads column b "Water-soluble zinc salts with the exception of zinc 4- hydroxy-benzene sulphonate (entry 25 of Annex III)" and names six substances in the glossary column: Zinc Acetate, Zinc Chloride, Zinc Gluconate, Zinc Glutamate, Zinc Citrate and Zinc Sulphate. Condition (d), "Other products", sets 1% (as zinc). Footnote 46 reads: "From 1 January 2027 cosmetic products containing these substances and not complying with the restrictions shall not be placed on the Union market. From 1 July 2028 cosmetic products containing these substances and not complying with the restrictions shall not be made available on the Union market." Checked 4 October 2026.