14 September 2008

Emulsion is the most vehicle used in sunscreen formula because it offers lots of advantages and wersality. Emulsion also offers highest SPF possible at the lowest possible cost. Emulsion has a uniform sunscreen film, thick sunscreen film, nontransparent sunscreen fil and minimum ingredient interaction with the sunscreen’s active agent.

Sunscreen Emulsions

Emulsions Advantages :
  • Sunscreen EmulsionGood performance in each of the important areas
  • Facilitate incorporation of sunscreen active agents, which are usually oils that can be easily emulsified
  • Can be prepared contain large percentage of water (more cost effective vehicle)
  • Cosmetically desirable vehicles (give skin smooth, silky, without being greasy)
  • Can accommodate a wide variety of raw materials
Emulsions Disadvantages :
  • Thermodynamically unstable
  • Eventually separate
  • Present a perfect medium for microbial contamination and require preservatives
Emulsions are classified in two categories Oil in water (O/W) and Water in Oil (W/O).

Water in Oil (W/O)
  • Better vehicle
  • Can be design as water resistant sunscreen and provide greater efficacy (higher SPF) for the same concentration as O/W emulsions.
  • Most sunscreens were soluble in the oil phase, that’s why in W/O emulsions the oil phase is continuous and when applied in the skin, there is no need for agglomeration to occur. A a result a very uniform sunscreen is produced during spreading, a long with a high SPF
Emulsions are often stabilized by liquid crystal. The liquid crystals are lamellar in structure and either form a gel network in the external phase or surround the oil droplets as layers. The liquid crystal structure reduces the tendency to coalesce because of the high viscosity of the lamellar structure and this facilitates high emulsions stability. Such emulsions are not very hydrophilic and provide water resistant characteristics for sunscreen formulations. Their lipoidal characteristics facilitate adhesion to the hydrophobic, lipoidal skin surface, and thus enable formation of a most uniform film.

Oil Advantages :
  • Sunscreen OilGenerally well accepted
  • Easy to formulate and easy to apply to the skin spreading quickly and uniformly to cover a large surface area
  • There is only one phase that’s why it has excellent product stability
  • Most sunscreen active agent are lipoidal in nature, they are soluble in the oils employed. Because of this, manufacturing process are more straightforward than the emulsion
  • Can be prepared in room temperature
Oil Disadvantage :
  • Thin and transparent sunscreen film, which will have a lower SPF
  • Poor performance by looking at the interactions between sunscreen (nonpolar ester) and the nonpolar oils vehicle (mineral oil). Nonpolar oil can cause the position of the UV curves to shift to shorter wavelength
  • The solubility parameter (stickiness/cohesiveness) determines orientation of the sunscreen within oil
  • Sunscreen oils are expensive system since the anhydrous oil system there is no water to lower the cost of expensive raw material

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