Patch Testing in Cosmetics — HRIPT / Closed Patch Studies

What Is Patch Testing?

Patch testing applies the product to a volunteer's skin under a closed plaster and assesses the skin reaction after removal. A single-application patch test investigates irritation potential; the repeat-application protocol (HRIPT) investigates sensitisation potential. HRIPT consists of an induction phase and a challenge phase.

Purpose of Patch Testing

The purpose is to show the product does not cause irritation or allergic sensitisation even under closed, exaggerated conditions. Closed application is a more demanding condition than normal use and provides a margin of safety.

Which Products Is Patch Testing Applied To?

Leave-on products
Facial and body creams
Deodorants and antiperspirants
Make-up products
Formulations with new ingredients

In Which Sectors Is Patch Testing Used?

CosmeticsChemistryRetail

Standards Related to Patch Testing

OECD TG 439 (in vitro skin irritation — complementary method)
OECD TG 442C/D/E (in chemico and in vitro sensitisation)
SCCS Notes of Guidance (safety assessment guidance)
TS EN ISO 10993-10 (irritation and sensitisation approach reference)

Patch Testing Conditions

Application: Occlusive (closed) or semi-occlusive plaster; contact time defined in the standard
HRIPT: Repeated application during the induction phase, a rest period, and the challenge application
Reading: At the defined time points after the plaster is removed
Ethics: Informed consent and ethical review are mandatory

Equipment for Patch Testing

Standard patch test plasters and chambers
Skin assessment scales and imaging
Chromameter and TEWL meter
Controlled application environment

Sample Requirements for Patch Testing

Market formulation
Sufficient specimen for the number of volunteers
Formulation and INCI list
Application concentration must be stated (with justification if it will be diluted)

Duration of Patch Testing

A single-application patch test spans application and reading days. HRIPT is markedly longer because of its induction, rest and challenge phases, and takes weeks.

Patch Testing Procedure

1The protocol is prepared and undergoes ethical review.
2Volunteers are selected and informed consent is obtained.
3The product is placed in the patch chamber at the defined amount and applied to the skin.
4The plaster is removed after the defined contact time.
5The skin reaction is assessed on a scale at the defined time points.
6In HRIPT, the challenge application is made after the rest period and read again.

Patch Testing Acceptance Criteria

The acceptance criterion is no unacceptable irritation or sensitisation reaction observed on the defined scale. In sensitisation assessment, a reaction pattern different from induction is looked for at the challenge stage.

Evaluation of Results

Closed application is more demanding than normal use; mild transient redness can be expected under this condition and is not on its own a non-conformity. The assessment relies on the scale and the dermatologist's interpretation. The number of volunteers determines the statistical power of the result. The test result alone does not establish compliance: (EC) 1223/2009 also requires appointing a responsible person, maintaining a Product Information File, having a qualified person carry out the safety assessment, and notifying the product to the CPNP. Laboratory data feeds into this file.

Patch Testing Report

Product identification and application concentration
Protocol type (single-application / HRIPT) and ethical approval
Number of volunteers and selection criteria
Application time and plaster type
Scale results for each reading point
Dermatologist's assessment

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

(EC) 1223/2009 Cosmetic Products Regulation
(EU) 655/2013 Common Criteria for Cosmetic Claims

Kozmetik Testleri — What Does This Testing Field Cover?

The section below describes the field that the Patch Testing test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Cosmetics testing shows that a product stays microbiologically safe throughout its use, delivers the performance it claims and contains no restricted substances. There is NO PRODUCT APPROVAL in this family: no authority approves a cosmetic product; responsibility rests entirely with the manufacturer and with the responsible person established in the EU.

This responsibility model shapes how the field works. Before the product is placed on the market a product information file (PIF) is prepared, a safety assessment (CPSR) is carried out and notification is completed. Inspection comes afterwards and asks for the file; if the file is incomplete the product is withdrawn from the market. Test reports form the evidence base of that file.

On the microbiological side there are two different questions and each is answered by a separate test. The CURRENT microbiological quality of the product is measured by enumeration and testing for specified microorganisms. The EFFECTIVENESS of the preservative system is examined by deliberately inoculating the product with microorganisms (challenge test): can the product resist repeated contamination throughout its use? A jar of cream is touched by a finger at every use; the preservative system must cope with that.

On the performance side, claim substantiation studies are carried out. For sunscreens, determination of SPF and UVA protection and measurement of water resistance are mandatory and are the basis of the value declared on the label. Evidence is also produced by in vivo or in vitro methods for claims such as moisturisation, appearance of wrinkles, hair care and colour retention.

On the chemical side, banned and restricted substances are screened: heavy metals, prohibited colorants, preservative concentrations, UV filter levels and contaminants such as nitrosamines. Products containing nanomaterials carry a separate notification obligation.

The BAN ON ANIMAL TESTING is the most defining constraint of the field. Animal testing cannot be carried out on finished products or ingredients, and a product tested on animals cannot be placed on the market. Alternative in vitro methods (reconstructed human skin models, cell culture based tests) are therefore at the centre of the field, and toxicological assessment rests largely on existing data, read-across approaches and in vitro results.

Stability and packaging compatibility studies determine shelf life and the period after opening (PAO). The interaction of the product with its packaging is also assessed: an active substance may migrate into the packaging, and substances that should not be present may pass from the packaging into the product.

On the process side, good manufacturing practice is demonstrated through ISO 22716; this is separate from product testing but a mandatory part of the file.

Method groups in this field

Microbiological quality
Enumeration of aerobic mesophilic bacteria, yeasts and moulds; testing for Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and E. coli.
Preservative efficacy
Resistance of the preservative system to repeated contamination by challenge test (ISO 11930).
Sun protection
In vivo SPF determination, in vitro UVA protection determination, water resistance and critical wavelength measurements.
Chemical analysis
Heavy metals, banned and restricted substances, quantification of preservatives and UV filters, contaminant screening.
Safety assessment
In vitro irritation and sensitisation methods, toxicological risk assessment, exposure calculations.
Stability and compatibility
Real-time and accelerated stability, packaging compatibility, PAO determination, sensory and physicochemical monitoring.

Commonly confused in this field

There is NO CE marking on cosmetics; conformity is demonstrated through the PIF, the safety assessment and notification.
The responsible person must be established in the EU; unless the exporter arranges this, the product cannot be placed on the market.
Microbiological quality and preservative efficacy are different tests; a product that comes out clean may still have a weak preservative system.
The animal testing ban covers ingredients too; animal test data generated for another market creates a problem of use.
An SPF claim must be supported by measurement; a formulation change requires a new measurement.
A change of packaging may require the stability and compatibility studies to be repeated.

Which decisions these results support

The product information file and the safety assessment
Verification of the preservative system design
Substantiation of SPF and efficacy claims
Determining shelf life and the period after opening
Compliance with destination market restrictions for export

Related Tests

Frequently Asked Questions About Patch Testing

Is HRIPT required for every product?

There is no mandatory list; the need depends on the outcome of the safety assessment. It is requested more often for leave-on products containing new ingredients or ones with unknown sensitisation potential. The qualified person carrying out the assessment determines the requirement.

How many volunteers are needed?

The number of volunteers is set by the protocol and the required level of evidence; sensitisation assessment requires a higher number than irritation assessment. The number is given in writing together with the protocol at the quotation stage.