Lotions are applied to external skin with bare hands, a brush, a clean cloth, cotton wool, or gauze. Many lotions, especially hand lotions and body lotions are formulated not as a medicine delivery system, but simply to smooth, re-hydrate, and soften the skin. These are particularly popular with the aging and aged demographic groups, and in the case of face usage, can also be classified as a cosmetic in many cases, and may contain fragrances.
Most lotions are oil-in-water emulsions using a substance such as cetearyl alcohol to keep the emulsion together, but water-in-oil lotions are also formulated. The key components of a skin care lotion, cream or gel emulsion (that is mixtures of oil and water) are the aqueous and oily phases, an emulgent to prevent separation of these two phases, and, if used, the drug substance or substances. A wide variety of other ingredients such as fragrances, glycerol, petroleum jelly, dyes, preservatives, proteins and stabilizing agents are commonly added to lotions. Lotions can be used for the delivery to the skin of medications such as:
- Anti-acne agents
- Soothing, smoothing, moisturizing or protective agents (such as calamine)
It is not unusual for the same drug ingredient to be formulated into a lotion, cream and ointment. Creams are the most convenient of the three but are inappropriate for application to regions of hairy skin such as the scalp, while a lotion is less viscous and may be readily applied to these areas (many medicated shampoos are in fact lotions). Historically, lotions also had an advantage in that they may be spread thinly compared to a cream or ointment and may economically cover a large area of skin, but product research has steadily eroded this distinction. Non-comedogenic lotions are recommended for use on acne prone skin.
Since thickness and consistency are key factors in lotions and creams, it is important to understand the manufacturing process that determines viscosity.
Manufacturing lotions and creams can be completed in two cycles: 1. Emollients and lubricants are dispersed in oil with blending and thickening agents. 2. Perfume, color and preservatives are dispersed in the water cycle. Active ingredients are broken up in both cycles depending on the raw materials involved and the desired properties of the lotion or cream.
A typical oil-in-water manufacturing process might go like this:
• Step 1: Add flake/powder ingredients to the oil being used to prepare the oil phase.
• Step 2: Disperse active ingredients.
• Step 3: Prepare the water phase containing emulsifiers and stabilizers.
• Step 4: Mix the oil and water to form an emulsion. (Note: This is aided by heating to between 110-185 F (45-85 C) depending on the formulation and viscosity desired.)
• Step 5: Continue mixing until the end product is uniform.
Careful note should be taken in choosing the right mixing equipment for lotion manufacturing to avoid agglomerates and long processing times. It can make all the difference in manufacturing time and costs. Conventional agitators can present a number of problems including agglomerates and longer processing times. On the other hand, high shear in-line mixers can produce quality lotions and creams without many of the complications encountered with conventional mixers. Sonolation is also a process that is growing in popularity.