D4 is a type of cyclic silicone oil. It is highly volatile and easily inhaled by the human body. There are reports that D4 may affect human reproductive ability, but there is no long-term research data that can 100% support this conclusion. At present, the cosmetics industry has been taking action, and Europe is conducting further safety assessments on silicone oil and D4. Major cosmetics companies will require raw material suppliers to provide D4 residues in some silicone oil raw materials and conduct standard control of D4 residues in raw materials. The D4 content in some silicone oil products may be as high as 1% or more. If it can be controlled below 0.1% or even less, the safety problems will be much less. D5 is not a residue, it is an approved cosmetic raw material ingredient. Due to its strong volatility, D5 will evaporate quickly during the use of skin care products made of D5, which can create the illusion of easy absorption and bring a refreshing skin feel. This simple and crude "easy absorption" technology makes it widely used in skin care products. However, large multinational cosmetics companies are currently looking for alternative ingredients for D5 to reduce safety concerns.