What Is Phenyl Mercuric Borate?
Phenyl Mercuric Borate is a synthetic compound that joins mercury, borate and a phenyl group to create a stable salt. Chemically it is known as dihydrogen orthoborato phenylmercurate. The ingredient was first explored in the early 1900s when researchers looked for ways to keep creams and lotions free of harmful bacteria. Because mercury could stop microbial growth, scientists combined it with borate to improve stability and lessen the sharp metallic odor common to older mercury salts.
Today the material is produced in a controlled lab by reacting phenylmercuric nitrate with a borate solution, then purifying the result to cosmetic grade. The final powder is white to off white and dissolves in water based mixes used by formulators.
You may find Phenyl Mercuric Borate in rinse off masks, certain cream cleansers, toners aimed at oil control, and some specialty anti blemish spot treatments. It is rarely used in leave on products meant for large areas of skin because modern rules limit mercury levels, but small amounts can still appear in niche formulations where broad spectrum microbial protection is critical.
Phenyl Mercuric Borate’s Cosmetic Benefits/Uses
This ingredient serves one clear purpose in personal care products: it works as a preservative. By slowing the growth of bacteria, mold and yeast it helps keep a formula safe and usable for its full shelf life. A well preserved product stays fresh longer, smells the way it should and lowers the risk of skin problems that can arise when microbes take hold.
Who Can Use Phenyl Mercuric Borate
Because Phenyl Mercuric Borate is included solely for preservation and at very low levels, it is technically suitable for normal, oily and combination skin. Sensitive or compromised skin may not tolerate it as well since mercury compounds can trigger irritation in reactive users. Dry skin is neither specifically helped nor harmed but may prefer formulas that use gentler modern preservatives.
The compound is synthetic and contains no animal derived materials so products using it are generally acceptable to vegans and vegetarians. That said, some consumers choose to avoid any ingredient that uses heavy metals for personal or environmental reasons.
Pregnant or breastfeeding individuals are often advised to avoid unnecessary exposure to mercury in any form. While the tiny amounts permitted in cosmetics are regulated and considered low risk, this is not medical advice and anyone who is expecting or nursing should review any product containing Phenyl Mercuric Borate with a qualified healthcare provider before use.
The ingredient does not make skin more sensitive to sunlight and there is no evidence that it interferes with sunscreen performance. It also plays no active role in treating or worsening acne so it can be present in both acne prone and non acne products purely for preservation.
Potential Side Effects/Adverse Reactions
Responses to topical Phenyl Mercuric Borate vary from person to person. The effects listed below are possible but unlikely for most users when the ingredient is used correctly in a well formulated product.
- Skin irritation – redness, stinging or itching can occur in people with sensitive or damaged skin
- Allergic contact dermatitis – rare immune reaction leading to rash or swelling at the application site
- Accumulation with prolonged use – very long term daily exposure on large areas could let trace mercury build up in the body
- Eye irritation – if a product accidentally enters the eye it may cause burning or watering
- Potential interaction with other mercury sources – using multiple products that each contain mercury compounds can raise overall exposure
If you notice any discomfort or unexpected reaction stop using the product immediately and consult a healthcare professional.
Comedogenic Rating
Rating: 0/5. Phenyl Mercuric Borate is water soluble and used at very low percentages purely for preservation, so it does not leave an oily film or block pores. It has no fatty acids or waxy carriers that typically trigger comedones, giving it a non-comedogenic profile. People prone to acne or breakouts can generally use products containing this preservative without worrying about clogged pores. If irritation occurs it would be from sensitivity to mercury rather than true comedogenicity.
Summary
Phenyl Mercuric Borate functions almost exclusively as a preservative, keeping creams, cleansers and masks free of bacteria, mold and yeast. The mercury portion disrupts microbial enzymes while the borate helps stabilize the compound so it stays effective throughout a product’s shelf life.
Because of strict limits on mercury in cosmetics the ingredient is now uncommon and usually appears only in niche or legacy formulas that rely on its broad spectrum power.
At the tiny levels allowed in finished products it is considered safe for healthy adults, though concerns about cumulative mercury exposure keep usage low. Anyone trying a product with Phenyl Mercuric Borate should perform a quick patch test first to be sure their skin tolerates it.