Angel dusting is the misleading marketing practice of including a minuscule amount of an active ingredient in a cosmetic, cosmeceutical, dietary supplement, food product, or nutraceutical, insufficient to cause any measurable benefit.  The advertising materials may claim that the ingredient is helpful and that the ingredient is contained in the product, both of which are true. However, no claim is made that the product contains enough of the active ingredient to have an effect – this is just assumed by the purchaser. Thus, while misleading, angel dusting is typically legal.
Manufacturers have several reasons not to include sufficient quantities to have a measurable effect. Consumers want the benefits of the active ingredient, but are unwilling to pay the cost or risk the side effects of that ingredient, while businesses want to maximize profit and minimize risk:
Cost. This ingredient may cost substantially more than other active or inactive ingredients. Thus, including a significant quantity would raise the price (which would decrease sales volume) and/or reduce the profit margin of the product.
Side effects. Effective ingredients also tend to have side effects. To minimize backlash from dissatisfied customers and possible lawsuits, yet still benefit from the appearance of including the ingredient, angel dusting may be employed. Ironically, the only way the consumer may know the quantity of the ingredient is from information supplied by the manufacturer while defending themselves from a lawsuit over side effects.
Insufficient labeling requirements. Consumer products generally are required to list ingredients, but not the quantities of each, which makes angel dusting difficult for the consumer to detect. A partial exception is in the area of food products, where some helpful ingredients, like vitamins, may have specific quantities listed, although others, like omega-3 fatty acids, may not.
Drug regulation: Chemicals that actually have an effect on the body are drugs and, as such, require extensive testing for safety and effectiveness. Drugs also require full listing of ingredients, with quantities, and may also require a prescription. Cosmetic companies wish to avoid their products having any actual physiological effect to avoid their being classified as drugs and put under this regime.