Ingredient review
Acid Green 25
INCI: CI 42170
A widely used synthetic dye that adds blue-green color to cosmetics; generally considered safe at low concentrations but offers no skincare benefit.
In plain English
CI 42170 is a man-made dye that gives a blue-green color to products like shampoo, soap, and makeup. It doesn't do anything for your skin—it's just there for appearance. Regulatory bodies have approved it for use in cosmetics at low levels, but some people may prefer to avoid synthetic colorants.
Review score
Safety, usefulness, and evidence
Potentially useful with some tradeoffs
The evidence base is useful, but some claims depend heavily on the formula.
Risk flags are low for most users, though the finished product can still irritate.
- Source
- synthetic
- Evidence
- moderate
- Irritation
- low
- Clogging risk
- low
Quick decision guide
Useful, but context matters
Acid Green 25 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.
- Step 1Start with the score, then check the irritation and clogging risk before judging Acid Green 25.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- 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
lowLess likely to sting, burn, or bother most users, though sensitive skin can still react.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
CI 42170 is a synthetic organic dye from the anthraquinone family, also known as Acid Green 25 or D&C Green No. 5. It is produced through chemical synthesis and is used to impart a blue-green hue to cosmetic formulations.
How it works
As a colorant, CI 42170 works by absorbing and reflecting specific wavelengths of visible light, creating the perception of a blue-green color. It is water-soluble and can be easily incorporated into aqueous and emulsion-based products.
Pros
Vibrant color
Provides a bright, stable blue-green shade that doesn't fade easily in light or over time.
Low irritation risk
At typical use levels, it rarely causes skin reactions, making it suitable for most people.
Cons and cautions
No skincare benefit
This ingredient is purely cosmetic—it adds color but does not moisturize, protect, or improve skin health.
Synthetic origin
Made from petrochemicals, which may be a concern for those preferring natural or sustainable ingredients.
Best for
- Anyone who wants colorful cosmetic products
- Consumers not concerned about synthetic colorants
Use caution if
- Individuals with known allergies to synthetic dyes
- Those seeking exclusively natural or organic products
Usage tips
Safety summary
CI 42170 is considered safe for use in cosmetics at typical low concentrations. Rare cases of skin irritation have been reported, but it is generally well-tolerated.
Research notes
Studies and regulatory reviews (e.g., FDA, SCCS) have concluded that CI 42170 is safe for cosmetic use at current levels. No significant health risks have been identified.
Common label clues
- Typical concentration
- Very low, typically less than 1%
- Regulatory status
- Approved for cosmetic use in the US (FDA) and EU (EC) with concentration limits in some product categories.
- Common uses
- Shampoos, Soaps, Bath products, Eye shadows, Lipsticks
- Environmental note
- As a synthetic dye, it may not be biodegradable and could contribute to water pollution if not properly treated in wastewater.
Good to know
- CI 42170 is approved for use in cosmetics in the US (as D&C Green No. 5) and the EU (as CI 42170).
- It is often used in combination with other dyes to create custom shades.
Common questions
What is Acid Green 25 in beauty products?
CI 42170 is a man-made dye that gives a blue-green color to products like shampoo, soap, and makeup. It doesn't do anything for your skin—it's just there for appearance. Regulatory bodies have approved it for use in cosmetics at low levels, but some people may prefer to avoid synthetic colorants.
What does Acid Green 25 do in a beauty product?
As a colorant, CI 42170 works by absorbing and reflecting specific wavelengths of visible light, creating the perception of a blue-green color. It is water-soluble and can be easily incorporated into aqueous and emulsion-based products.
Is Acid Green 25 safe for most people?
CI 42170 is considered safe for use in cosmetics at typical low concentrations. Rare cases of skin irritation have been reported, but it is generally well-tolerated.
Who should be careful with Acid Green 25?
Individuals with known allergies to synthetic dyes Those seeking exclusively natural or organic products
Research sources
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.