The word pearlescence (Merriam-Webster Dictionary) first appears in the English language in 1936 and is defined as "having a pearly appearance." The word pearly dates back to the 15th century and is described as "resemblling, containing, or adorned with pearls or mother-of-pearl." It seems to be a rather difficult trait to precisely describe, but never the less it is an appearance that has been sought by cosmetic chemists and marketers for many years. While formulators of shampoos know how to achieve this effect (with varying degrees of success), the growing popularity of body washes and 2-in-1 shampoos has made this product form ubiquitous. The appearance we are talking about is opalescence.