It can be frustrating to decipher the long chemical names on the label of your favorite cosmetic products. Simple ingredients like water and alcohol are easy to recognize. But lengthy chemical names can leave even the most conscious consumers scratching their heads.

Cyclopentasiloxane (D5) is used in hundreds of cosmetics. In the past, there was controversy about its potential health and environmental risks. But the Cosmetic Ingredient Review Expert Panel considers it safe to use in cosmetics. However, in early 2018 the European Union introduced restrictions on D5 use in cosmetic products that are intended to be washed off before evaporation. Concentrations above 0.1% in wash-off products were determined to have a risk of accumulating in the water supply.

Read on to learn more about this common cosmetic ingredient and how it might affect you and the environment.

Cyclopentasiloxane is a silicone regularly used in cosmetic products. It’s commonly found in medical implants, sealants, lubricants, and windshield coatings.

D5 is colorless, odorless, non-greasy, and water-thin. It doesn’t get absorbed into the skin. Rather, it evaporates quickly away from it. This property makes it a useful ingredient in cosmetic products that need to dry quickly, like antiperspirants and hair sprays.

It also has lubricating properties. This gives a slippery and silky feeling when applied to the skin and hair and allows the product to spread more easily.

D5 is known for being able to evaporate and dry quickly. Silicones are also known to repel water and glide easily. This is why they are commonly used as ingredients in lubricants and sealants.

They are also known to form a protective barrier on the skin and hair. This can help you detangle your hair, prevent breakage, and reduce frizz.

D5 can be found in a wide range of personal care products. Examples include:

  • hair spray
  • sunscreen
  • antiperspirant
  • deodorant
  • hair conditioner
  • shampoo
  • hair detangling products
  • waterproof mascara
  • foundation
  • eyeliner
  • concealer
  • moisturizer with SPF
  • eye shadow
  • hairstyling gel and lotion
  • lipstick

It sometimes appears on a label as decamethylcyclopentasiloxane or D5. It may also be put under the broader category name of cyclomethicone.

It’s different from another siloxane known as dimethicone or polydimethylsiloxane (PDMS).

One of the main benefits of D5 compared to similar ingredients is that it’s less expensive. This helps lower the cost of your favorite products. Of course, the lower cost means there’s an incentive for manufacturers to use it instead of other ingredients, regardless of its safety or environmental impact.

Safety concerns in humans

The Environmental Working Group (EWG) found that there’s a low concern that D5 can be considered an endocrine disrupter, or something that can disturb the normal functioning of your hormones. It could be more of a concern when it’s used at concentrations higher than what is typically used in cosmetics. The Cosmetic Ingredient Review Expert Panel considers the chemical safe to use at existing concentrations.

To be an endocrine disruptor, a chemical must get into the body. A 2012 study published in the International Journal of Toxicology found that D5 isn’t absorbed into the skin. A 2016 study confirmed that it rapidly evaporates after contacting the skin with very little of the chemical entering the body.

If inhaled, it’s either quickly exhaled or broken down and excreted in urine. This means that accumulation of this chemical in the body is unlikely.

D5 also wasn’t found to cause skin irritation or sensitization in humans. When used in sunscreens and lotions, research shows it may even prevent irritation in patients with skin conditions like rosacea.

Environmental hazards

There is some controversy surrounding the environmental impact of this ingredient. Chemicals used in hair and skin products can make their way into the environment when they’re rinsed down the drain. These products may then accumulate and harm fish and other wildlife.

Cyclopentasiloxane was once considered hazardous to aquatic wildlife. It was found in laboratory studies to be bio-accumulative in some aquatic animals. This prompted a Canadian review board to conduct more research about the environmental impact of this chemical.

A 2011 review concluded that D5 didn’t pose a danger to the environment. The review board found no evidence of toxicity to any organism. The board also didn’t find evidence that the chemical can build up to high enough concentrations to cause problems in animals.

A 2013 study found that the chemical evaporates during typical use. Only a very small fraction of the chemical finds its way down the drain and into the environment. This amount is considered negligible by the study authors.

Contrary to the earlier studies, recent evaluation by the European Union regarding environmental accumulation of D5 has resulted in limits on concentrations used in wash-off cosmetics to less than 0.1%, effective January 31, 2020.

Products containing cyclopentasiloxane can be used safely on your hair and skin with minimal personal risk. It helps your skin and hair products dry quickly and spread more easily. It can make the hair feel silky without weighing it down.

Though there is a concern that this ingredient can disrupt hormones in your body, research shows that it doesn’t get absorbed into the skin in high enough doses to cause harm.

It is possible that D5 could accumulate in water supplies when used in concentrations above 0.1% and when washed off before evaporating. This possibility has led to increased regulation of its use in some countries.