What is a demulcent in eye drops?

A demulcent is a lubricating ingredient in an eye drop. FDA’s over-the-counter ophthalmic rules, 21 CFR 349.3, define it as an agent, usually a water-soluble polymer, applied to the eye to protect and lubricate its surface and relieve dryness and irritation. Section 349.12 lists the approved ones, including glycerin and polysorbate 80, two of Quell’s three actives.

The definition in the regulation

The rules for over-the-counter eye drops are in Title 21 of the Code of Federal Regulations, part 349. Section 349.3 holds the definitions. It describes a demulcent as “an agent, usually a water-soluble polymer, which is applied topically to the eye” to “protect and lubricate mucous membrane surfaces and relieve dryness and irritation.”

In plain terms, a demulcent is a soothing, slippery ingredient that sits on the eye’s surface. On a Drug Facts panel, the purpose column usually says “lubricant” rather than “demulcent,” because that’s the word most people know.

Which ingredients count as demulcents

Section 349.12, “Ophthalmic demulcents,” lists the active ingredients a lubricating eye drop may use under the monograph, each with its own allowed concentration range. They fall into a few groups:

• Cellulose derivatives: carboxymethylcellulose sodium, hydroxyethyl cellulose, hypromellose and methylcellulose.
• Dextran 70, allowed only together with another polymer demulcent.
• Gelatin.
• Liquid polyols: glycerin, polyethylene glycol 300, polyethylene glycol 400, polysorbate 80 and propylene glycol.
• Polyvinyl alcohol.
• Povidone.

If you turn over a box of lubricating eye drops and read the active ingredients, you’ll almost always find something from this list.

Quell’s demulcents

Two of Quell’s actives come from the liquid polyols group: Glycerol (1.0%) and Polysorbate 80 (1.0%). Glycerol is another name for glycerin, the name the regulation uses. Quell’s label gives both the purpose “lubricant.” Glycerol in eye drops and polysorbate 80 in eye drops cover each one.

Demulcent vs. emollient

The third active in Quell, Light Mineral Oil (0.5%), isn’t a demulcent. It falls under a separate section, 349.14, “Ophthalmic emollients.” Section 349.3 describes an emollient as an agent, “usually a fat or oil,” used “to protect or soften tissues.” Light mineral oil appears in 349.14’s list of oleaginous, or oily, ingredients, alongside mineral oil, paraffin, petrolatum and waxes. Lanolin preparations make up the other emollient group.

So a lubricating eye drop can carry two kinds of ingredient: water-friendly demulcents and oily emollients. Quell carries both, which suits its design: it is designed to reinforce the tear film’s oil layer to help reduce moisture loss, and the tear film itself has a watery layer under an oily one.

Why demulcents are active ingredients

On a Drug Facts panel, an ingredient listed under Active ingredients is one that does the drug’s stated job. For a lubricating eye drop, the demulcents and emollients are that job. Everything else is listed under Inactive ingredients; Quell’s are Caprylyl Glycol, Dead Sea Salt (Sodium Chloride), Emu Oil, Glyceryl Laurate, Glyceryl Undecylenate, Manuka Honey, Polaxamer 188, Sterile Water, Terminalia Chubula and Tromethamine. The active ingredients section explains how that part of the label is laid out.

What the Uses line says demulcents are for

The monograph also sets the wording a demulcent product may use to describe its purpose, in section 349.60. Quell’s Uses line is one of those permitted statements: For use as a protectant against further irritation or to relieve dryness of the eye. What does “protectant” mean on eye drops? unpacks that wording.

Questions worth asking a pharmacist

• Which demulcent is in each drop I’m comparing, and does the difference matter for me?
• Does this drop also contain an emollient, and what does that add?
• Is there anything in the inactive ingredients I should watch for, given my allergies?
• How should I space this drop around any other eye products I use?

A pharmacist can read a Drug Facts panel with you in a minute or two, and these questions turn a list of chemical names into something you can act on. Bring the bottle or a photo of the label so they can see the exact wording.

Reading demulcents on any label

• Look at the Active ingredients box first. Lubricating drops list their demulcents there, each with a concentration.
• Compare concentrations only for the same ingredient; different demulcents work in different amounts.
• Check whether the drop also lists an emollient, which tells you it includes an oily component.
• Read the Inactive ingredients for preservatives if that matters to you. Quell has none.

If you have questions about whether a particular demulcent suits you, or how it fits with other drops you use, ask your pharmacist or eye doctor. Quell’s full panel is on the Drug Facts page.