Ingredient review

Acid Blue 9 Ammonium Salt

INCI: Acid Blue 9 Ammonium Salt

A widely used synthetic blue dye that adds color to cosmetics but offers no skincare benefits.

beautyskincarecolorant

In plain English

Acid Blue 9 Ammonium Salt is a man-made blue dye. It's the same color you might see in some blue candies or drinks, but in skincare and makeup, it's used to make products look more appealing. It doesn't do anything for your skin—it's purely cosmetic.

Quick decision guide

Useful, but context matters

Acid Blue 9 Ammonium Salt is generally a lower-concern ingredient when the full formula suits your skin.

Plain-English read

Treat this as a practical screening step before you compare products that contain this ingredient.

  1. Step 1Start with the score, then check the irritation and clogging risk before judging Acid Blue 9 Ammonium Salt.
  2. Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
  3. Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.

Score terms in plain English

Irritation risk

low

Less likely to sting, burn, or bother most users, though sensitive skin can still react.

Clogging risk

low

Less likely to feel heavy or contribute to clogged pores for most skin types.

Evidence level

moderate

There is useful support, but formula details and claim strength still matter.

What it is

A synthetic, water-soluble blue dye derived from petroleum. It belongs to the triphenylmethane family of colorants and is approved for use in cosmetics in many regions.

How it works

It works by absorbing and reflecting specific wavelengths of light, making the product appear blue. It does not interact with the skin's biology.

Pros

Vibrant color

Provides a bright, consistent blue shade that doesn't fade easily in most formulations.

Widely approved

Approved for cosmetic use by major regulators including the FDA and EU, with a long history of safe use.

Cons and cautions

No skincare benefit

This ingredient is purely decorative—it adds color but does not hydrate, protect, or improve skin health.

Potential staining

Can temporarily stain skin, nails, or fabrics, especially in high concentrations or in leave-on products.

Best for

  • Anyone who enjoys colorful makeup or bath products
  • People looking for a consistent, stable blue shade

Use caution if

  • Those with known sensitivity to synthetic dyes
  • People seeking purely natural or organic cosmetics

Usage tips

Use in rinse-off products like bath bombs or soaps to minimize staining risk.
Patch test a colored product on a small area of skin before full use if you have sensitive skin.

Safety summary

Generally considered safe for topical cosmetic use at typical concentrations. Rare cases of contact dermatitis have been reported. Avoid contact with eyes.

Research notes

Studies confirm low acute toxicity and low skin irritation potential. Long-term safety data is based on decades of use rather than extensive clinical trials.

Common label clues

Typical concentration
Very low (typically less than 1%)
Regulatory status
Approved for cosmetic use in the US (FDA), EU, and many other countries. Subject to concentration limits in some regions.
Common uses
Eyeshadows, Lipsticks, Soaps, Bath products
Environmental note
As a synthetic dye, it is not biodegradable and may accumulate in waterways. Proper disposal of products containing it is recommended.

Good to know

  • Often listed as 'Blue 1' or 'CI 42090' on labels.
  • In some countries, this dye is also used in food and pharmaceuticals.

Common questions

What is Acid Blue 9 Ammonium Salt in beauty products?

Acid Blue 9 Ammonium Salt is a man-made blue dye. It's the same color you might see in some blue candies or drinks, but in skincare and makeup, it's used to make products look more appealing. It doesn't do anything for your skin—it's purely cosmetic.

What does Acid Blue 9 Ammonium Salt do in a beauty product?

It works by absorbing and reflecting specific wavelengths of light, making the product appear blue. It does not interact with the skin's biology.

Is Acid Blue 9 Ammonium Salt safe for most people?

Generally considered safe for topical cosmetic use at typical concentrations. Rare cases of contact dermatitis have been reported. Avoid contact with eyes.

Who should be careful with Acid Blue 9 Ammonium Salt?

Those with known sensitivity to synthetic dyes People seeking purely natural or organic cosmetics

Research sources

FDA Color Additive Status ListOpenCosIng Database - Acid Blue 9OpenPubMed - Safety of Triphenylmethane DyesOpen

Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.