De Veiligheidsmarge in cosmetische toxicologie, eenvoudig uitgelegd

If you have ever read a Cosmetic Product Safety Report and wondered what the columns of numbers in the toxicology section are for, they are almost certainly margins of safety. The margin of safety is the central calculation in cosmetic toxicology, and it sits inside the safety assessment format set out in Annex I of Regulation (EC) No 1223/2009 and its UK equivalent under the Cosmetic Products Enforcement Regulations 2013. It is also the engine inside a Toxicological Risk Assessment for products that are not cosmetics. Regulators such as the Office for Product Safety and Standards expect to see it, and the European Commission's Scientific Committee on Consumer Safety (SCCS) sets out how it is done in its Notes of Guidance.

 

This article explains the margin of safety in plain English: what goes into it, why 100 is the magic number, how exposure is estimated, what it does and does not cover, and a worked example. You will not need to calculate one yourself, but you will understand why your assessor asks for the numbers they do and why some ingredients are capped at levels that feel low.

The idea in one sentence

A margin of safety compares how much of an ingredient it takes to cause harm with how much a person actually gets from the product, and asks whether the gap between the two is comfortably large. If the harmful dose is a thousand times the dose you receive, the margin is a thousand and the ingredient is not a concern at that level. If the harmful dose is only twenty times what you receive, the margin is twenty, and the assessor will either restrict the ingredient or refuse to sign.

The two numbers

The NOAEL: how much is safe in studies

The no observed adverse effect level is the highest dose of a toxic substance at which toxicology studies, usually repeated dose studies in animals or reliable human data, found no adverse effect. It is expressed per kilogram of body weight per day. The assessor takes it from published toxicological profiles, regulatory opinions and supplier data. Where no NOAEL exists, an equivalent threshold or a read across from a similar substance may be used with appropriate caution, and where the substance has no safe threshold at all, for example a genotoxic carcinogen, the margin of safety approach does not apply and the substance is simply not acceptable.

The systemic exposure dose: how much you actually get

The systemic exposure dose, or SED, is the estimated amount of the ingredient that enters the body each day from using the product as intended. It brings together five things: how much product is applied per day for that product type, the concentration of the ingredient in the product, how much of the applied ingredient is absorbed through the skin, the frequency of use, and the body weight of the user. Assessors use standard daily application amounts published in the scientific committee's guidance for each product type, such as a body lotion, a face cream or a shampoo, and a default body weight, typically sixty kilograms for an adult.

The formula

Margin of safety equals NOAEL divided by systemic exposure dose. The systemic exposure dose itself is the daily amount of product applied, multiplied by the concentration of the ingredient, multiplied by the fraction absorbed through the skin, divided by body weight. Units matter: the NOAEL is in milligrams per kilogram per day, so the SED must be too.

Why 100?

The benchmark margin of 100 is the product of two safety factors of 10. The first allows for the possibility that humans are more sensitive than the animals in which the NOAEL was established. The second allows for variation between people: children, the elderly, people with compromised skin and the generally more susceptible. A margin below 100 does not automatically mean a product is dangerous, but it means the assessor cannot demonstrate safety with the usual level of confidence and will normally require the ingredient level to come down.

A worked example

Imagine a body lotion containing a preservative at 0.5 percent. The published NOAEL for that preservative is 500 milligrams per kilogram of body weight per day. Guidance gives the daily amount of body lotion applied as roughly 7.8 grams. Dermal absorption data are unavailable, so the assessor uses a conservative default of fifty percent. The body weight is sixty kilograms.

• Amount of ingredient applied per day. 7.8 grams of lotion at 0.5 percent is 39 milligrams of preservative.
• Amount absorbed. Fifty percent of 39 milligrams is 19.5 milligrams.
• Systemic exposure dose. 19.5 milligrams divided by 60 kilograms is 0.325 milligrams per kilogram per day.
• Margin of safety. 500 divided by 0.325 is about 1,540.

A margin of about 1,540 is comfortably above 100, so the preservative at 0.5 percent is acceptable on systemic grounds in this product. Now imagine the same preservative in a product used in far greater quantity, or at two percent, or with a hundred percent absorption assumption, and the margin shrinks quickly. Raise the preservative to 2 percent and the margin falls to about 385. Assume full absorption at 2 percent as well and it drops to about 190, still above 100 but with far less room. This is why the same ingredient can be fine in one product and restricted in another.

Aggregate exposure and the whole routine

A careful assessor also considers that people use more than one product. An ingredient present in a face cream, a body lotion and a hand cream from the same routine adds up, so guidance provides aggregate exposure values that assume a full daily routine, and the margin of safety for widely used ingredients is judged against that total rather than a single product. It is one reason preservatives and UV filters, which appear in many products, carry regulatory concentration limits set with aggregate exposure in mind.

What the margin of safety does not cover

The MoS is about systemic toxicity, adverse effects that follow absorption into the body. It says nothing about whether an ingredient will irritate the skin or eyes, sensitise, or cause a phototoxic reaction. Those local effects are assessed separately, using irritation and sensitisation data, IFRA and regulatory limits, and specific tests where needed. A product can have enormous margins of safety on every ingredient and still fail its assessment because a fragrance is a sensitiser at the level used or a cold pressed citrus oil is phototoxic. Both halves have to pass.

Environmental hazard, worth noting, is a separate question again: it concerns aquatic life and ecosystems rather than the person using the product, and it sits under a different part of the assessment entirely when it is relevant at all.

Where the margin of safety appears in your documents

In a Cosmetic Product Safety Report, the margin of safety calculations sit in Part A, section 8, alongside the toxicological profile of each ingredient with a systemic endpoint, as the Commission's CPSR guidelines (Implementing Decision 2013/674/EU) describe. Part B is where the assessor states the conclusion those numbers support, together with any warnings or conditions of use. Our guides to CPSR Part A and CPSR Part B walk through both halves. In a Toxicological Risk Assessment for a non cosmetic product, the same calculation appears in the risk characterisation, with the exposure model adjusted for inhalation or other routes. Either way, the presence of clear, sourced margins of safety is one of the marks of a report that will stand up to scrutiny.

Reading the margin of safety table in your report

Section 8 of Part A usually presents the calculation as a table with one row per ingredient assessed for systemic effects: the ingredient, its concentration, the daily product amount, the dermal absorption value used, the resulting systemic exposure dose, the NOAEL with its source, and the margin of safety. Rows with very high margins, often in the thousands, are ingredients present at trace levels or with generous NOAELs. Rows in the low hundreds are the ones that constrained the formula, and if you ever want to raise an ingredient's level, those are the rows that will decide whether you can. Ingredients not in the table are typically those assessed as having no systemic concern, such as large polymers that do not cross the skin, or those handled by regulatory limits and local effect data rather than MoS. If a row is missing for an ingredient you expected to see, ask why; a good assessor will have a reason recorded.

Where the NOAEL comes from

The quality of a margin of safety depends on the quality of the NOAEL behind it. The best sources are repeated dose toxicity studies over ninety days or longer, reviewed by a regulatory scientific body such as the European scientific committee for consumer safety, whose opinions on preservatives, UV filters, hair dyes and other ingredients are the assessor's first port of call. Where no committee opinion exists, the assessor turns to peer reviewed literature, industry safety dossiers and supplier toxicological summaries, weighing each for reliability. Where data are thin, a NOAEL may be borrowed from a structurally similar substance, called read across, or a very conservative default threshold may be applied. Each choice is recorded with its source in Part A, because a margin of safety is only as defensible as the number it starts from.

Dermal absorption: the biggest lever in the calculation

Of all the inputs, dermal absorption moves the result most. If good experimental data show that only two percent of an ingredient crosses the skin, the systemic exposure dose falls fifty fold compared with an assumption of one hundred percent, and the margin of safety rises fifty fold with it. In the absence of data, assessors use conservative defaults: typically fifty percent, or one hundred percent for small, lipophilic molecules and for products applied to compromised skin or mucous membranes. This is why suppliers of active ingredients invest in absorption studies, and why an assessor may permit a higher level of an ingredient with a solid absorption dossier than of a similar ingredient with none. It is also why lip products, applied to a mucous membrane and partly swallowed, are assessed with high absorption assumptions and correspondingly tighter limits.

Children, pregnancy and other sensitive users

The standard sixty kilogram adult does not describe every user. For products aimed at babies and young children, the assessor recalculates with a child's body weight and a larger surface area to weight ratio, which raises the systemic exposure dose sharply for the same product and concentration. Some committee opinions set separate, lower limits for children's products for exactly this reason. Products marketed for pregnancy avoid ingredients with reproductive or developmental endpoints regardless of margin. If your product is for a specific vulnerable group, say so before the assessment starts, because the exposure model and the acceptable ingredient levels change with the user.

Why this matters to you as a maker

You will never be asked to calculate a margin of safety, but understanding it explains most of the constraints an assessor places on a formula. It is why a fragrance can be used at one level in a rinse off wash and a fraction of that in a leave on oil. It is why ingredient percentages have to be exact, not approximate. It is why the assessor asks what the product is and how it is used before looking at a single ingredient, because the daily amount applied changes everything. And it is why an assessor will sometimes ask you to reduce an ingredient that is perfectly legal, because legal limits are ceilings and the margin in your particular product may still be too thin.

• Give exact percentages. An approximate formula produces an approximate margin, and assessors will not sign on approximations.
• Describe the use honestly. A product marketed for all over daily use is assessed at much higher exposure than a spot treatment.
• Expect limits below the legal maximum. Legal limits are ceilings; your product's exposure may justify a lower level.
• Understand that natural is not exempt. Every ingredient with a systemic endpoint gets the same calculation.

If you are designing a formula and want to know in advance which ingredients are likely to constrain it, an expert consultation before you finalise the recipe is far cheaper than reformulating after the assessment.

Myths we hear

• If an ingredient is legal at a percentage, it is safe at that percentage in my product. Legal limits are ceilings. At your use level and exposure, the margin of safety can still fall below 100, so the assessor may set a lower limit.
• Natural ingredients do not need a margin of safety. Every ingredient with a systemic endpoint gets the same calculation, whether it is synthetic or plant derived.
• A high margin of safety means the product cannot irritate or sensitise. The margin of safety covers systemic effects only. Irritation, sensitisation and phototoxicity are assessed separately.

What to do this week

1. Send your assessor exact percentages for every ingredient, not ranges.
2. Describe exactly how, where and how often the product is used.
3. Flag products for babies, children or pregnancy before the assessment starts.
4. Ask suppliers for dermal absorption data and toxicological summaries for key actives.
5. Read the margin of safety table in Part A, section 8, and note which rows constrain your formula.
6. Book a consultation before finalising the recipe if you plan high levels of preservatives, actives or fragrance.

Frequently asked questions

Official sources and legislation

• Regulation (EC) No 1223/2009 on cosmetic products, Annex I
• Cosmetic Products Enforcement Regulations 2013
• Office for Product Safety and Standards
• European Commission cosmetics pages, including the scientific committee
• SCCS Notes of Guidance for the testing of cosmetic ingredients and their safety evaluation (12th revision)
• Commission Implementing Decision 2013/674/EU, guidelines on Annex I (CPSR)