1. Anti-caking Agent – Prevents lumps from forming in food due to excess water. They usually function as a water repellent or by absorbing excess moisture
2. Anti-foaming Agent / Defoamer – Reduces or hinders the formation of foam
3. Drug / Medicine – Used to treat, alleviate, cure or prevent sickness. As officially declared by a governmental drug/medicine regulatory body
4. Emollient – Softens and soothes the skin. Prevents water (moisture) loss from the skin
5. Lubricant – Prevents or reduces friction
6. Surfactant – Reduces the surface tension to allow mixtures to be formed evenly. Emulsifier is a specific type of surfactant which allows two liquids to mix together evenly
Dimethicone (also called polymethylsiloxane) is a silicon-based polymer used as a lubricant and conditioning agent. Its applications range from contact lenses and medical devices to elastomers; it is also present in shampoos (as dimethicone makes hair shiny and slippery), food (antifoaming agent), caulking, lubricants and heat-resistant tiles.
Activated dimethicone, a mixture of polydimethylsiloxanes and silicon dioxide (sometimes called simethicone), is often used in over-the-counter drugs as an antifoaming agent and carminative. It has also been at least proposed for use in contact lenses.
PDMS is used variously in the cosmetic and consumer product industry as well. For example, PDMS can be used in the treatment of head lice on the scalp and dimethicone is used widely in skin-moisturizing lotions where it is listed as an active ingredient whose purpose is “skin protection.” Some cosmetic formulations use dimethicone and related siloxane polymers in concentrations of use up to 15%.
PDMS compounds such as amodimethicone, are effective conditioners when formulated to consist of small particles and be soluble in water or alcohol/act as surfactants (especially for damaged hair), and are even more conditioning to the hair than common dimethicone and/or dimethicone copolyols. 
It is approved to use as food additive in EU (E900A).
Recent Findings :
Short-term dermal dosing of dimethicone on rabbits in concentrations ranging from 6-79% resulted in no adverse effects. Dimethicone was also given orally/dermally to rats, rabbits and monkeys and other than a minor decrease in body weight, no adverse effects were detected. Dimethicone was negative for all reproductive and developmental toxicity studies and in all genotoxicity assays. Even an oral dose of 91% given to mice showed no signs of carcinogenicity. 
Dimethicone is also used to improve gastrointestinal tolerability of non-steroidal anti-inflammatory drugs (NSAIDs) like ketoprofen. Dimethicone prevents gastric lesions and does not alter the bioavailability (the % of drug absorbed) of the drug. 
4% Dimethicone solutions is also used to cure head louse infections in 89 out of 127 (70%) participants.  In a similar study, 141 out of 145 (97%) of children aged 5-15 were cleared of head louse infections after application of a dimethicone solution for 9 days. 
Environmentally, >99% of dimethicone is removed via sewage sludge, which is then incinerated to produce inorganic silica, water and carbon dioxide. Biological degradation involves dimethicone coming in contact with “clay minerals” in the soil which also results in silica, water and carbon dioxide. 
Overall, dimethicone is generally safe even in high doses. It is an effective pediculicide (substance used to treat lice) and it alleviates the side-effects of NSAIDs. Lastly, it decomposes easily to mild substances.
Scientific References :
1. PubChem: https://pubchem.ncbi.nlm.nih.gov/compound/24705
2. Final report on the safety assessment of stearoxy dimethicone, dimethicone, methicone… (Int. J. Toxicol. 22(2 Suppl), 13-35 DOI:10.1177/1091581803022s204)
3. Effect of dimethicone (polysilane gel) on stereoselective pharmacokinetics of ketoprofen (Eur J Clin Pharmacol (1998) 54: 351±354 DOI:10.1007/s002280050473)
4. Treatment of head louse infestation with 4% dimeticone lotion: randomised controlled equivalence trial (BMJ. 2005 Jun 18;330(7505):1423 DOI:10.1136/bmj.38497.506481.8F)
5. A highly efficacious pediculicide based on dimeticone: Randomized observer blinded comparative trial (BMC Infectious Diseases 2008, 8:115 DOI:10.1186/1471-2334-8-115)
6. Environmental fate and effects of dimethicone and cyclotetrasiloxane from personal care applications (Int J Cosmet Sci 20, 297–305 (1998) DOI:10.1046/j.1467-2494.1998.181595.x)
Regulatory References :
1. EU Approved Food Additive