Ingredient review

Phenolsulfonphthalein

INCI: Phenolsulfonphthalein

Phenolsulfonphthalein is a synthetic dye used in tiny amounts for color; it has no proven skincare benefits and is generally safe at low concentrations.

beautyskincarecolorant

In plain English

Phenolsulfonphthalein, also known as Phenol Red, is a man-made dye that changes color depending on the acidity (pH) of the product. In skincare, it's added in very small amounts to give a specific shade or to help formulators check the pH. It doesn't moisturize, exfoliate, or treat any skin condition—it's purely a colorant.

Review score

Safety, usefulness, and evidence

2.5Fair
2.5/ 5

Higher-caution ingredient

The evidence base is still emerging, so marketing claims deserve extra caution.

Risk flags are low for most users, though the finished product can still irritate.

Source
synthetic
Evidence
emerging
Irritation
low
Clogging risk
low
How reviews are scored

Quick decision guide

Read the cautions before using

Phenolsulfonphthalein 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 Phenolsulfonphthalein.
  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

emerging

The ingredient may be promising, but claims should be treated more cautiously.

What it is

A synthetic organic compound belonging to the triphenylmethane dye family, used as a pH indicator and cosmetic colorant.

How it works

In cosmetics, it dissolves in water and imparts a red-to-yellow color depending on the pH. It does not interact with skin cells or provide any active benefit; its role is strictly visual or for formulation quality control.

Pros

Stable color

Provides a consistent, predictable color in formulations without fading or reacting with other ingredients.

Low irritation risk

At the very low concentrations used in cosmetics, it rarely causes skin irritation or allergic reactions.

Cons and cautions

No skincare benefit

It does not hydrate, brighten, or improve skin health—it's purely a colorant with no active function.

Synthetic origin

Some consumers prefer to avoid synthetic dyes due to personal or environmental concerns, even though it is considered safe at low levels.

Best for

  • Anyone using color cosmetics where this dye is present at low levels
  • Formulators needing a reliable pH indicator

Use caution if

  • Individuals with known sensitivity to synthetic dyes
  • Those seeking active skincare ingredients

Usage tips

Check the full ingredient list if you have a known sensitivity to synthetic dyes.
Use products containing this ingredient only as part of your color cosmetic routine, not for therapeutic skincare.

Safety summary

Phenolsulfonphthalein is considered safe for cosmetic use at low concentrations. There is no evidence of significant irritation, sensitization, or toxicity in topical applications. However, it offers no active skincare benefit.

Research notes

Research on phenolsulfonphthalein in cosmetics is limited; most studies focus on its use as a pH indicator in laboratory settings. No peer-reviewed studies confirm any skincare efficacy.

Common label clues

Typical concentration
Very low (typically less than 0.1%)
Regulatory status
Approved as a color additive in cosmetics in the EU and US when used within concentration limits. Not intended for use on broken skin or near eyes.
Common uses
Color cosmetics, pH-adjusting formulations
Environmental note
As a synthetic dye, it may not biodegrade quickly. Disposal should follow local regulations for chemical waste.

Good to know

  • Phenolsulfonphthalein is also used in medical diagnostics as a kidney function test dye.
  • It is not a common ingredient in most mainstream skincare; you'll more often find it in specialty or lab-grade formulations.

Common questions

What is Phenolsulfonphthalein in beauty products?

Phenolsulfonphthalein, also known as Phenol Red, is a man-made dye that changes color depending on the acidity (pH) of the product. In skincare, it's added in very small amounts to give a specific shade or to help formulators check the pH. It doesn't moisturize, exfoliate, or treat any skin condition—it's purely a colorant.

What does Phenolsulfonphthalein do in a beauty product?

In cosmetics, it dissolves in water and imparts a red-to-yellow color depending on the pH. It does not interact with skin cells or provide any active benefit; its role is strictly visual or for formulation quality control.

Is Phenolsulfonphthalein safe for most people?

Phenolsulfonphthalein is considered safe for cosmetic use at low concentrations. There is no evidence of significant irritation, sensitization, or toxicity in topical applications. However, it offers no active skincare benefit.

Who should be careful with Phenolsulfonphthalein?

Individuals with known sensitivity to synthetic dyes Those seeking active skincare ingredients

Research sources

Cosmetic Ingredient Review (CIR) Safety AssessmentOpenPubChem - PhenolsulfonphthaleinOpenEuropean Chemicals Agency (ECHA) InformationOpen

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.