What Is Guanine?
Guanine (listed on labels as CI 75170) is a crystalline substance best known for the pearly, light-reflecting sparkle it gives to cosmetics. It was first noticed in fish scales in the 19th century, which led early formulators to collect those scales to create “pearl essence” for perfumes and powders. Today manufacturers mostly produce guanine in labs or recover it from sustainable fish-processing by-products, then purify and mill it into a fine, shimmering powder.
Chemically, guanine belongs to the same family of molecules found in DNA, yet in cosmetics its value is entirely visual. The flat, plate-like crystals reflect light much like tiny mirrors, giving a soft sheen or a bold sparkle depending on how much is used.
You will spot guanine in products that need that eye-catching glow: pressed and loose eyeshadows, highlighters, illuminating foundations, lipsticks, nail polishes, shimmering body lotions, hair gels, bath bombs and some whitening toothpastes. Because it can also cloud a formula for a pastel finish, it turns up in creams and lotions where a rich, opaque look is desired.
Guanine’s Cosmetic Benefits/Uses
In everyday beauty products guanine serves two main jobs that both revolve around how it handles light.
- Colorant – The sparkling white crystals scatter and reflect light, adding a pearlescent or metallic effect that makes shades look livelier and skin appear more radiant
- Opacifying agent – By diffusing light inside a formula it reduces transparency, giving creams, lotions and makeup a creamy, even appearance that helps hide blemishes and enhances coverage
Who Can Use Guanine
Guanine is considered suitable for most skin types including dry, normal, combination and oily skin. Its particles sit on the surface rather than sinking into pores so it rarely troubles acne-prone or sensitive complexions. Very sensitive or highly reactive skin may still prefer to keep overall shimmer levels low since any particulate ingredient can cause mechanical irritation if overused.
Because traditional guanine is harvested from fish scales it is not automatically vegan or vegetarian friendly. Many brands now use lab-created or certified by-product sources that never involve live animal harvesting, so consumers following a cruelty-free or plant-based lifestyle should check the label or ask the manufacturer for sourcing details.
No specific warnings exist for pregnant or breastfeeding women regarding topical guanine. It is regarded as an inert, non-penetrating color additive. Still, this is not medical advice and anyone who is pregnant or nursing should show the full ingredient list of any cosmetic to their healthcare provider for personalized guidance.
Guanine does not increase photosensitivity and has no known interactions with UV exposure. It can be worn safely during the day with or without sunscreen, though standard sun protection habits remain important for overall skin health.
Potential Side Effects/Adverse Reactions
Responses to topical guanine vary from person to person. The issues below are possible yet uncommon when the ingredient is used correctly by reputable manufacturers and most people will experience none of them.
- Mild skin irritation
- Contact allergy presenting as redness itching or rash
- Eye irritation if loose powder or aerosolized product enters the eye
- Aggravation of existing dermatitis if applied to broken or highly inflamed skin
If any of these effects occur stop using the product and consult a healthcare professional for assessment and advice.
Comedogenic Rating
Rating: 0/5
Guanine crystals are inert, non-oil based particles that remain on the skin’s surface rather than mixing with sebum or settling into pores. Because they do not create a film or feed acne-causing bacteria they have virtually no pore-clogging potential, earning a solid zero on the comedogenic scale.
People prone to acne or frequent breakouts can generally use products containing guanine without extra concern. If a guanine-containing formula does trigger congestion it is far more likely due to other ingredients such as heavy oils or waxes.
Summary
Guanine’s main jobs in cosmetics are to add pearlescent color and to reduce transparency for a creamier look. Its plate-like crystals scatter light, which creates the unmistakable shimmer seen in eyeshadows, highlighters, lipsticks and even everyday lotions. It is moderately popular: prized in makeup lines that favor glow yet skipped in fully vegan ranges unless a synthetic version is used.
Overall guanine is considered very safe for topical use with low irritation and no comedogenic risk. Still, skin can be unpredictable, so it is smart to patch test any new product that features this sparkling additive before applying it all over.