5-Free, 7-Free, 10-Free Nail Polish — What Do These Numbers Mean, and Do They Matter?

On drugstore shelves, nail polishes compete with numbers: 5-free, 7-free, 10-free, and some brands even claim 21-free. To a shopper this sounds like a safety guarantee — the higher the number, the better. But is it really? To answer that question, we need to start at the beginning: with the substances that genuinely raised legitimate concerns.

The Toxic Trio — the three ingredients that started it all

The term "Toxic Trio" emerged in the 2000s, when consumer organizations drew attention to three ingredients commonly used in nail polishes:

• Toluene — a solvent that ensures smooth application. Chronic occupational exposure (e.g. in a salon without ventilation) is linked to headaches, respiratory irritation, and potential neurotoxic effects. ECHA classifies it as a reproductive toxicant, category 2.
• Formaldehyde — a hardener that improves the durability of the film. The IARC (International Agency for Research on Cancer) classified it in Group 1 — a confirmed human carcinogen. It was used in polishes at concentrations of up to 5%, which, with regular contact, can sensitize and irritate the nail bed.
• DBP (dibutyl phthalate) — a plasticizer that adds flexibility. It acts as an endocrine disruptor — in animal studies, it disturbed hormonal balance following prenatal exposure. The EU limits its concentration in cosmetics to 0.001%.

A polish labeled 3-free contains none of these three substances. That was the first step — and, it must be said, a scientifically justified one.

From 5-free to 7-free — a reasonable expansion

The 5-free formula additionally eliminates:

• Camphor — at high concentrations it can trigger allergic reactions and is potentially toxic when inhaled.
• Formaldehyde resin (tosylamide/formaldehyde) — a formaldehyde derivative and a strong contact allergen; it accounts for a significant share of contact dermatitis around the nails.

The 7-free variant adds two more:

• Xylene — an irritant solvent with a profile similar to toluene.
• Ethyl tosylamide — a film-forming agent that drew controversy because of its synthetic origin from sulfonamides (although the evidence for its harmfulness is weak).

Up to this point, the list of bans still has some grounding in toxicological data — though not every one of these substances is equally problematic.

10-free, 15-free, 21-free — the point where marketing takes over

The deeper you go, the more substances land on the "banned" list — but many of them aren't used in polishes anyway or are already regulated under EU law. Examples from 10-free and higher lists:

• Parabens — preservatives common in creams, but practically unheard of in classic nail polishes (polish doesn't require microbiological preservation in the traditional sense).
• Gluten — it isn't absorbed through the nail plate, so its presence or absence has no dermatological significance.
• Ingredients of animal origin — this is an ethical issue, not a toxicological one, and it conflates two entirely different topics.

A study published in Contact Dermatitis (2019) found that many brands using the 10-free claim replace the excluded substances with ingredients that have an even less well-studied safety profile. In other words: removing a known substance does not automatically mean the replacement is safer.

What does EU law say?

Regulation (EC) No 1223/2009 on cosmetic products already bans or strictly regulates most of the substances that "free" labels warn about. Free formaldehyde is limited to 0.2% (as an impurity in resins), toluene is not permitted as an intentional ingredient, and DBP is practically eliminated from legal production.

This means that a polish bought in a Polish drugstore — even without any "free" claim — must meet the same safety standards. A 10-free label offers no additional legal protection; it offers an additional marketing argument.

What should you really pay attention to?

Instead of counting numbers on the packaging, it's worth focusing on what actually matters:

1. Ventilation — the biggest risk associated with polishes is inhaling solvent fumes. Paint your nails in a well-ventilated room.
2. Frequency of contact — a nail technician working 8 hours a day has a completely different risk profile than someone who paints their nails once a week.
3. Analyzing the full composition — instead of trusting simplified labels, check a product's INCI list in the PurScore ingredient database. That way you'll see what's actually in the formula, not just what isn't.
4. Substitute resins and plasticizers — check whether the replacements (e.g. diisodecyl adipate, TPHP — triphenyl phosphate) have sufficient safety data. Read our guide to the INCI list to learn how to interpret a composition.

The bottom line

The 3-free and 5-free claims had a sound toxicological basis and helped push substances with proven risks off the market. Beyond that threshold, each additional number has less and less to do with science and more and more to do with marketing. The best strategy? Don't count how many ingredients were removed — check what was put in their place.