Why has my Korean skincare changed colour?

Your new serum looks a little darker than the bottle you just finished. Or the vitamin C on your bathroom shelf has turned a deeper yellow. It is understandable to wonder whether something is wrong, especially when you have paid for a product you trust.

A colour difference can have several explanations. Ingredients may give a formula its natural tint, while a change over time can signal oxidation or deterioration. Before deciding whether to keep using it, check what the brand says about that specific product.

First, is it a different batch or a change in the same bottle?

Start with when you noticed the difference. If a new bottle looks different from your previous purchase, check the batch and product version. If the same bottle has changed while you have been using it, consider where you store it and how long it has been open.

Botanical ingredients can vary with growing and harvesting conditions. Research on plant extracts collected at different times has demonstrated differences in their properties.^[1] Natural raw materials are not always identical. The acceptable colour range for a finished serum still needs to come from its manufacturer.

There is no single rule that makes every colour variation across Korean skincare normal. Check the guidance for your formula rather than applying one brand's explanation to everything on your shelf.

Anua: a pink serum can get its colour from an ingredient

Anua explains the pink tint of its Peach 70 Niacin Serum on its official product page:

“Natural pink color from VITAMIN B12 with no artificial coloring.” ^[2]

That pink tint is part of the formula. Anua's explanation does not cover every possible change in colour, so a bottle that fades or darkens noticeably still deserves a check.

Anua Peach 70 Niacin Serum 30ml

• Skin type: Dry or dehydrated skin seeking hydration and a more radiant appearance.
• Ingredients: Peach fruit extract, 5% niacinamide, hyaluronic acid and vitamin B12.
• Benefits: A lightweight serum for moisture, dullness and uneven-looking texture.
• How to use: Apply two to three drops after cleansing and toning, avoiding the eye area. Follow with moisturiser and sunscreen during the day.

Anua's published ingredient list includes fragrance, so keep that in mind if your skin is fragrance-sensitive.^[2] View Anua Peach 70 Niacin Serum at RuZu Beauty.

COSRX: vitamin C darkening needs a different explanation

Pure vitamin C behaves differently from a formula's naturally pink tint. COSRX explains that air, UV exposure, pH and temperature can contribute to oxidation. Its vitamin C guide describes the colour becoming:

“a dark yellow color, which might even turn brown” ^[3]

A pronounced change towards dark yellow or brown deserves attention. Do not assume it is harmless botanical variation. Compare it with the manufacturer's expected appearance and follow the storage and use-period instructions for your exact bottle.

There is also no universal shade chart for all vitamin C serums. Their starting colours and formulations differ, so an online photo of another product cannot tell you how much active vitamin C remains in yours.

COSRX The Vitamin C 23 Serum 20ml

Currently out of stock at RuZu Beauty. Included here to explain vitamin C oxidation.

• Skin type: Experienced vitamin C users targeting dullness, uneven tone and post-breakout marks. High-strength vitamin C may be too much for easily irritated skin.
• Main ingredient: 23% pure vitamin C. Check your pack for the full ingredient list, particularly when comparing older and newer versions.
• Benefits: Targeted brightening care in a concentrated serum.
• How to use: COSRX advises two to three drops after cleansing and toning, followed by moisturiser and daytime SPF. Introduce gradually according to tolerance.

The current official COSRX page lists a two-month period after opening. Follow your own product's label and storage instructions, especially if it differs from the current version online.^[4] View COSRX The Vitamin C 23 Serum at RuZu Beauty.

When should you pause and check?

Check more than the shade. Has the smell or texture changed too? Is the product still within its use period, and has it been stored properly? The US Food and Drug Administration explains that heat, sunlight and air can change colour and texture, while emulsions can separate and preservatives can deteriorate.^[5]

Stop using the product and contact the seller if you notice a major unexplained colour change, an unusual smell, unexpected persistent separation, visible growth or new irritation. Do not patch test a product you suspect is spoiled to try to prove it is safe.

Some formulas are deliberately made in layers, so separation must also be assessed against the product's instructions. Shaking a damaged formula does not establish that it is usable.

How to store skincare through a South African summer

A sunny bathroom shelf or a hot car is a poor place for skincare. The FDA specifically warns that heat can make preservatives break down and encourage microbial growth.^[5]

• Keep products away from direct sunlight and heat.
• Close lids promptly and keep applicators clean.
• Write the opening date on products with a short use period.
• Follow each brand's refrigeration instructions. A skincare fridge is not a universal requirement.

Does a colour difference mean my skincare is fake?

You cannot authenticate skincare by colour alone. Check who sold it to you and keep your purchase record. The exact product version and batch details also help the seller or brand investigate a concern.

If you bought from RuZu Beauty and something looks different, send us your order number, clear photos of the product and packaging, the batch code and expiry date. Let us know when you opened it and how it has been stored. Message our team on WhatsApp at 076 723 2895 so we can review the concern and advise on the next step.

Quick answers

Does “no artificial colouring” mean a serum should be clear?

No. Anua's Peach serum gets its pink appearance from vitamin B12.^[2]

Can skincare deteriorate before its expiry date?

Yes. Storage and handling affect shelf life, and the period after opening may end before the printed expiry date.^[5]

Should I keep using a serum that suddenly turns brown?

Pause and check with the seller or manufacturer. For pure vitamin C, COSRX identifies darkening towards brown as a feature of advancing oxidation.^[3]

Sources

Official brand guidance and supporting research checked on 17 October 2026. Manufacturer information may change as formulas are updated.

1. Multifunctional Profiling of Moringa oleifera Leaf Extracts for Topical Application: A Comparative Study of Different Collection Time. Primary research, indexed in PubMed. Supports variability in botanical raw materials, rather than a colour or safety specification for the products featured here.
2. Anua: Peach 70% Niacinamide Serum. Official product page, natural colour explanation, ingredients and directions.
3. COSRX: All about VITAMIN C. Official brand guide to vitamin C and oxidation.
4. COSRX: Advanced The Vitamin C 23 Serum. Official current product information, directions and period after opening.
5. US FDA: Shelf Life and Expiration Dating of Cosmetics. General stability, handling and storage guidance, used here for product-care information rather than South African regulatory advice.