How is the Systemic Exposure Dose calculated under the SCCS Notes of Guidance?

There are two equations and the one that applies depends on how the dermal absorption study reported its result. If absorption is given as an absolute amount in micrograms per square centimetre, SED equals DAa multiplied by ten to the minus three, multiplied by the skin surface area, multiplied by the frequency of application, divided by body weight, with 60 kg as the SCCS default. If absorption is given as a percentage of the applied dose, SED equals the relative daily exposure multiplied by the concentration divided by one hundred, multiplied by the absorption percentage divided by one hundred.

What is an acceptable Margin of Safety for a cosmetic ingredient?

The Margin of Safety is the point of departure divided by the Systemic Exposure Dose, and the threshold used in cosmetic safety assessment is 100. A value below 100 means the exposure is not adequately justified at that concentration, and the formulation, the concentration or the exposure assumptions need to be revisited.

Should the frequency of application be multiplied into the exposure calculation?

Not on the percentage route. The daily amounts in Tables 3A and 3B already contain the frequency of use, because the underlying consumer study did not separate frequency from amount per application. Frequency is used on the surface area route, and when a daily amount is built up from an amount per event. If the real number of applications differs from the standard assumption, the Notes of Guidance requires the exposure figure to be adapted explicitly.

Why does the relative daily exposure not equal the daily amount divided by 60 kg?

The footnotes to Tables 3A and 3B state that the relative figures use the actual body weights of the people in the use study rather than the 60 kg default. Back-calculating from the published rows gives implied weights between about 58 and 70 kg depending on the product, so the relative daily exposure must be read from the table rather than computed.

Which cosmetic products have no default exposure amount in the Notes of Guidance?

Bath oils and salts, eau de toilette spray, perfume spray, shaving cream and aftershave appear in Table 4 with a surface area and a frequency of application but have no daily amount in Tables 3A, 3B or 5. For these the safety assessor has to establish and justify the exposure values case by case. Hand wash soap is a partial case: it has no Table 3A row, but Table 5 gives a daily exposure of 0.20 grams per day and 3.33 milligrams per kilogram of body weight per day.

Notes of Guidance, 12th revision · SCCS/1628/21

SCCS Dermal Exposure & Margin of Safety Calculator

Calculate the Systemic Exposure Dose and Margin of Safety for a cosmetic ingredient using the default exposure values published by the Scientific Committee on Consumer Safety. Choose a product and the daily amount, retention factor, skin surface area and frequency of application are filled in from Tables 3A, 3B, 4 and 5. Every figure can be overridden, and every figure carries the table it came from.

Product categories: 26
Reference tables: 3A · 3B · 4 · 5
SED equations: 4 and 5
MoS threshold: 100

Product

Choose the area treated, then the product within it. The reference values below fill automatically.

Area of application

Product type

Leave-on or rinse-off

Other routes to assess separately

Dermal absorption result

Section 3-3.5.4 gives two equations for the Systemic Exposure Dose, and which applies depends on how your absorption study reported its result rather than on the product. Your choice dims the inputs that do not apply.

Surface area route

SED = DAa × 10⁻³ × SSA × f_appl ÷ bw. Frequency of application and body weight are live on this route, with 60 kg as the SCCS default.

Skin surface area, SSA cm²

Frequency, f_appl per day

Dermal absorption, DAa µg/cm² your study data

Target population

Percentage route

SED = E_product/bw × C/100 × DAp/100. Skin surface area and frequency play no part here, because the frequency of use is already contained inside the published daily amount.

Daily amount applied, q_x g/day

Retention factor, f_ret

Relative daily exposure mg/kg bw/day

Dermal absorption, DAp % your study data

Relative daily exposure is read from the table, never divided by the body weight selected above. Tables 3A and 3B used the actual weights of the people in the underlying use study, which works out between 58 and 70 kg depending on the product.

Substance

Use the maximum concentration permitted in this product category, and the point of departure from your toxicological dossier.

Concentration in the finished product, C % your formulation

Point of departure, PoD_sys mg/kg bw/day your toxicological dossier

How this calculator works

The SCCS Notes of Guidance sets out two routes to a Systemic Exposure Dose, and the one that applies depends on how your dermal absorption study reported its result rather than on the product being assessed.

Where absorption is given as an absolute amount in micrograms per square centimetre, equation 4 applies and the calculation needs the skin surface area from Table 4, the frequency of application, and a body weight, with 60 kg as the SCCS default for adults. Where absorption is given as a percentage of the applied dose, equation 5 applies and the calculation needs the relative daily exposure from Table 3A, 3B or 5, the concentration of the substance in the finished product, and the absorption percentage. The two routes draw on different inputs, which is why this tool asks which result you hold before it asks for any numbers.

Three points reliably catch people out. Frequency of application is already contained inside the daily amounts published in Tables 3A and 3B, because the underlying consumer use study did not separate frequency from amount per application, on the assumption that the two are inversely correlated for regularly used products. The percentage route must therefore not multiply by frequency a second time. Relative daily exposure is likewise a published figure tied to the body weights of the people in that study rather than a division of the daily amount by 60 kg, so changing the target population does not rescale it. And several product categories appear in Table 4 with a surface area and a frequency but carry no daily amount anywhere in the Notes of Guidance, which means the safety assessor has to establish and justify those values rather than borrow them from a neighbouring product.

This is a first-tier deterministic screen. It does not cover probabilistic higher-tier assessment, aggregate exposure across several product categories, inhalation or oral exposure, or local endpoints such as irritation and sensitisation. Results should be reviewed by a qualified safety assessor before they are relied upon in a Cosmetic Product Safety Report.

Reference values reproduced from the SCCS Notes of Guidance for the Testing of Cosmetic Ingredients and their Safety Evaluation, 12th revision (SCCS/1628/21), Tables 3A, 3B, 4 and 5, and sections 3-3.4.2.1, 3-3.5.4 and 3-5.1. Calculator © Phoenix Safety Consultants Private Limited.