Arbutin, which occurs in bearberry along with methyl arbutin, hydrolyses to hydroquinone and glucose. Effective agents for specific areas include corticosteroids, tretinoin, and hydroquinone. Skin lightening creams have commonly contain mercury, hydroquinone, and corticosteroids. Hydroquinone, benzenetriol and catechol are converted to polyphenols. Key products include vanillin and ethylvanillin, but also hydroquinone or catechol. They can oxidise catechol to 1,2-benzoquinone and hydroquinone to 1,4-benzoquinone. Subsequent oxidation of the hydroquinone gives the quinone. Other hydrogen-bonded networks are derived from hydroquinone, urea, and thiourea. It can be stabilized with hydroquinone or hydroquinone ethyl ether. The useful dye quinizarin is produced by diacylation of hydroquinone with phthalic anhydride. The common products used were hydroquinone and corticosteroids. In the United States, topical treatments usually contain up to 2% in hydroquinone. The compound is typically stored with hydroquinone, which inhibits polymerization. The principal irritants are derivatives of farnesyl hydroquinone and 3-farnesyl-P-hydroxybenzoic acid. Alternatively, efforts to lighten the unaffected skin, such as with hydroquinone, may be tried.