A serum is one of the most profitable items in a personal-care range and one of the least forgiving to manufacture. The fill volume is small, the active load is high, and the packaging is usually a dropper or an airless pump — three things that interact badly with a rushed development process. This guide covers what buyers and brand owners should decide before a serum goes into production.

First: decide what the product legally is

This matters more than the formula. In most markets a face serum is a cosmetic, not a supplement, even when it contains vitamins or botanicals. That changes the labelling rules, the allowed wording and the compliance route. A serum may describe what it does to the surface of the skin and how it feels, but it may not claim to treat a medical condition, and it may not borrow supplement-style claims just because the active is also sold in a capsule. Agree the classification with your manufacturer and take local advice before artwork.

Choose the base before the actives

The base sets the viscosity, the feel and how much active the formula can carry:

  • Water-based gel serums — the most common type. Light, fast-absorbing, and the easiest base for water-soluble actives such as niacinamide, hyaluronic acid and most vitamin C derivatives.
  • Emulsion serums — a light oil phase dispersed in water. Good for combining water- and oil-soluble actives, but they need an emulsifier system and are harder to keep stable.
  • Anhydrous (oil-based) serums — no water, so no preservative is strictly needed. Excellent for oil-soluble actives and for sensitive formulas, but the feel is heavier.
  • Ampoule concentrates — single-dose glass or plastic. Highest cost per millilitre, best for oxygen-sensitive actives.

Once the base is fixed, the target viscosity decides the filling equipment and the packaging: a thin gel flows well into a dropper bottle but will not hold in an airless pump without adjustment.

Actives: pick for compatibility, not just for the label

Every active brings its own pH window, solubility and stability limit. Practical examples:

  • L-ascorbic acid — the most effective form of vitamin C and the most difficult: it needs a low pH, is sensitive to oxygen and light, and turns colour as it oxidises. Many brands choose a derivative instead and accept a lower potency for a much more stable product.
  • Niacinamide — water-soluble, stable across a wide pH range, and easy to combine. High percentages can cause flushing in some users, so the level is a marketing and tolerance decision.
  • Hyaluronic acid — available in several molecular weights; the combination of high and low weights changes the feel more than the percentage does.
  • Tranexamic acid — water-soluble and usually paired with niacinamide; keep it inside its solubility limit or it will recrystallise.
  • Retinol — effective at low percentages and the most fragile of the group: it needs antioxidant protection, light-proof packaging and an oxygen-controlled fill.
  • Peptides — sensitive to the preservative system and to pH extremes; test the finished formula, not the active alone.

Preservation and stability are the real test

Any water-containing serum needs a preservative system and a preservative efficacy (challenge) test to prove it works. Then the finished product needs stability data:

  1. Accelerated and real-time stability at the actual pack, checking pH, viscosity, colour and assay over time.
  2. Pack compatibility — the formula must be tested in the container you intend to sell, including the dropper or pump mechanism, because some actives attack certain plastics and elastomers.
  3. Microbiology on the finished batch, not only on the raw materials.

Shortcutting this stage is how serums reach customers brown, separated or contaminated three months after launch.

Packaging and fill

  • Dropper bottles — 30 ml is the standard size, with 15, 50 and 100 ml variants. Good value and easy to fill; the trade-off is that every opening exposes the formula to air.
  • Airless pumps — better protection for oxidation-sensitive actives and a more premium feel, but they need a viscosity-matched formula and a higher unit cost.
  • Ampoules and single-dose vials — the best barrier, the highest cost. Suitable for concentrates and for travel formats.

Choose the pack before finalising the formula, not after. Changing from a dropper to an airless pump late in development usually means reformulating.

MOQ, sampling and lead times

Serum development is a small-batch activity by nature, so trial volumes are usually modest. A practical starting point with a manufacturer that supports small batches is MOQ 500 units per SKU, samples in 3–5 days, production shipped within 7 days, and a certificate of analysis with every batch. See our serums and ampoules range for the standard pack options.

How Haiyue Shengda works

We develop and fill serums, masks, creams, cleansers and cosmetics alongside our supplement lines in our own 5,000+ m² factory with 7 production lines and 34 machines, under FDA facility registration and HACCP, cGMP and ISO 22000. Custom formulations and outer-packaging design are free, with the first design sketch in about two hours. Browse serums, read the FAQ, or contact us — we reply within one hour on working days.