Description

What is 4-Butylresorcinol?

4-Butylresorcinol — also known as Rucinol, CAS 18979-61-8 — is a high-purity brightening active supplied as a white to off-white crystalline powder. It is a butyl-substituted resorcinol with the formula C₁₀H₁₄O₂ and a molecular weight of 166.22, assayed at ≥ 99.0 % by HPLC.

It works on the pigmentation pathway at several points at once: it competitively inhibits tyrosinase and TRP-1, interferes with the glycosylation and uptake of tyrosinase, and reduces the transfer of melanosomes to keratinocytes. The butyl chain also makes the molecule markedly more lipophilic (log P 2.8), which is what separates it from plain resorcinol and improves its penetration into the skin. Because it acts at the source of melanin production rather than on already-deposited pigment, it is used for dark spots, uneven tone and the marks left behind by blemishes.

Key Benefits

• Blocks melanin at the source. It inhibits tyrosinase and TRP-1 competitively and disrupts the uptake and transfer of tyrosinase, so dark spots are addressed where pigment is produced rather than after it has settled in the skin.
• Calms skin and fades acne marks. Beyond pigment control it moderates the inflammatory response, which makes it practical for blemish-prone skin and for the red-to-brown marks left after acne.
• Stronger than the usual resorcinol brighteners. The butyl chain raises lipophilicity and enzyme binding, and published comparisons at equal use level put 4-butylresorcinol ahead of hexylresorcinol and phenylethyl resorcinol on spot fading.
• Effective at very low addition. Most leave-on formulas use 0.1 – 0.5 %, so the active cost per unit, and the load on the rest of the formula, stay low.
• A hydroquinone-free route to even tone. It delivers visible brightening without the irritation, phototoxicity and cytotoxicity concerns that restrict hydroquinone, and it supports the formula as an antioxidant and anti-glycation active as well.

FAQ

• What use level do you recommend? 0.1 – 0.5 % covers most leave-on skincare. The catalogue range for this grade is 0.1 – 5 %; the final level must be checked against the permitted maximum and the claims allowed in the target market.
• How does it differ from hexylresorcinol or hydroquinone? Hexylresorcinol belongs to the same resorcinol family and works through similar steps; 4-butylresorcinol is the more lipophilic, more potent member. Hydroquinone is a different chemistry with irritation and phototoxicity constraints — 4-butylresorcinol is the hydroquinone-free option for daily leave-on products.
• Can it be combined with niacinamide or tranexamic acid? Yes, and it is common practice. These actives interfere with different steps of the pigmentation pathway, so the combination typically outperforms either ingredient alone.
• How should it be added to a formula? Pre-dissolve it in propylene glycol, PEG-8 or a polar ester, then add to the oil phase or post-emulsify below 40 °C. Keep the finished product in a sealed, light-protected container; no pH adjustment is needed.