Drugs need to be soluble in both polar and nonpolar environments. The relative solubility of a drug in these environments is important to its absorption, distribution and excretion. If a drug is too polar, its polarity can be reduced by removing or masking polar functional groups. If polar functional groups are removed, it is important to remove only those groups that are not part of the pharmacophore. The polar functional groups usually masked in the prodrug approach are alcohols, phenols and carboxylic acids. Alcohols and phenols are usually masked using an acetyl group, while carboxylic acids are usually masked as a methyl or ethyl ester. Prodrugs with different solubility properties to the parent drug can sometimes be used to target a drug to particular parts of the body. The prodrug is highly polar, due to the presence of a carboxylic acid and phenol.