Testing

Why testing sits inside the process, not after it

Testing is stage four of the formulation process and continues into the regulatory check at stage five. Running stability work while samples are still being refined means the sample the client approves is one that has already shown it holds its properties, and the packaging it will be sold in has been part of the test.

Stability and shelf life

Stability testing exposes the formulation to defined storage conditions over time and records whether its properties change. The observations usually include:

• Appearance and colour: darkening, fading, clouding, precipitation.
• Odour: fragrance drift or off-notes that signal degradation.
• Texture and viscosity: thinning, thickening, loss of foam.
• Physical stability of emulsions: separation, creaming, oiling-out.
• pH: drift that can affect actives and skin compatibility.
• Actives: whether sensitive ingredients such as vitamin C derivatives or retinoids remain within their expected range.

Accelerated conditions (elevated temperature, and cycles between heat and cold) give an early read; real-time conditions confirm the assigned shelf life. Products in Singapore’s climate and in export markets are assessed with those storage conditions in mind.

Packaging compatibility

The same tests are run with the product in its primary packaging, because containers can interact with a formulation: some plastics absorb fragrance or oils, some actives degrade with light or air, and some closures affect preservation. This is why packaging is selected during formulation rather than after it (see packaging and branding).

Microbial quality and preservation

Cosmetic products must be protected against microbial growth during their shelf life and during use. The preservation system is designed into the formulation, and finished products are controlled for microbial quality under the GMP quality system, which covers quality control and release of every batch.

Safety and claims support

A cosmetic product must be safe for its intended use, and the notification behind it rests on a product information file that includes a safety assessment. Where a brand wants to make a specific claim - for example about hydration over a stated period - the test that would substantiate it is identified at the concept stage and agreed in the development plan. Ingredient supplier data supports the choice of an active; it does not by itself substantiate a claim for the finished product.

What is agreed per project

Testing depth depends on the product, the actives and the claims. The development plan for each project states which tests are run, under which conditions, and what the acceptance criteria are, so that the brand knows what supports the product before production is scheduled.

Frequently asked questions

What does stability testing check?

That the product keeps its physical, chemical and microbiological properties over its intended shelf life. Typical observations are appearance, colour, odour, viscosity, pH, phase separation in emulsions and the condition of key actives, recorded at intervals under controlled storage conditions.

How long does stability testing take?

Accelerated conditions give an early indication within weeks; real-time studies run for the intended shelf life. The development plan states which conditions and durations apply to your product and how the shelf life will be assigned.

Is every product tested on people?

Cosmetic products must be safe for their intended use, and a safety assessment is part of the product information behind notification. Tests involving volunteers, such as compatibility or efficacy studies, are arranged when a claim or a product type requires them and are agreed in the development plan.

Written by

Celcode Dermal Lab

Published

10 September 2026

Updated

15 October 2026