Propanediol(in 9,999 products)
1. Emollient - Softens and soothes the skin. Prevents water (moisture) loss from the skin.
2. Humectant - Binds with water to increase skin hydration. Also enhances water absorption of the skin
3. Solvent (Cosmetics) - Enhances the properties of other ingredients
4. Viscosity Controlling Agent - Maintains or alters the thickness of a liquid, mostly used in cosmetics
Propanediol is a three-carbon diol that is clear or very slightly yellow, odorless liquid. it is derived from corn sugar and is considered as an alternative to propylene glycol for those who want products that don't contain petroleum-based glycols. Propanediol exists in two common forms, 1,2-propanediol (propylene glycol) and 1,3-propanediol. 
Propanediol (PDO) is a common ingredient in cosmetics and personal care products such as lotions, cleansers, and other skin treatments. Some companies will use it in their moisturizer formulation due to its effectiveness and relatively low cost. It is also an excellent solvent to dissolve other active ingredients and a viscosity reducer to make the cosmetics easier to apply onto the skin. 
Propanediol exists in two main chemical forms, 1,2-propanediol (also known as propylene glycol) and 1,3-propanediol. For the purposes of this research, propanediol refers to 1,3-propanediol.
Although propanediol has traditionally been processed and obtained from glycerol/glycerin, new studies have gone into making eco-friendly and renewable versions of propanediol. In research conducted by DuPont, propanediol polymer fibers can be made from corn sugar (Sorona®), which reduces greenhouse gas emissions by up to 40% and has similar fiber functionality compared to the petrochemical variant. 
It can also be made from enzymes and bacteria (such as Klebsiella, Clostridia and Citrobacter) and genetic engineering experimentation is underway to make the conversion to of biofuels to propanediol more efficient. 
DuPont has also made Zemea® for commercial purposes. It can be used as a humectant or emollient and “Zemea bio-derived 1,3-propanediol can replace petroleum-based glycols such as propylene glycol (PG), butylene glycol (BG) or glycerin.” and “Zemea propanediol is the world’s first 100% natural glycol alternative approved by ECOCERT and certified by the Natural Products Association”.  "In multiple studies using the modified Draize Repeated Insult Patch Test method, Zemea® propanediol produced no skin irritation, fatigue or sensitization—even at high concentrations." and "Researchers observed no clinically significant dermal irritation or allergic contact following exposure of up to 75% Zemea® propanediol at three different pH levels."  "Results from these studies show that Zemea® propanediol has low potential to irritate or sensitize human skin." 
Propanediol has a "widespread history of use for properties such as humectancy, moisturization or emulsification".  In animal studies conducted on rabbits (Draize method), propanediol has shown to be "mildly irritating". In guinea pigs, propanediol shows "no dermal irritation or sensitization".
An acute irritation dermal study was conducted on 40 healthy, Japanese volunteers and "no significant skin irritation was observed". It is generally presumed that propanediol shows a "lack of or low potential for dermal irritation and sensitization of skin". 
1. PubChem: https://pubchem.ncbi.nlm.nih.gov/compound/134919
2. A New Polymer Platform for the Future — Sorona® from Corn Derived 1,3-Propanediol. (J. Polym. Environ., 13(2), 159–167. doi:10.1007/s10924-005-2947-7)
3. Microbial production of 1,3-propanediol: Recent developments and emerging opportunities. (Biotechnol. Adv., 27(6), 895–913. doi: 10.1016/j.biotechadv.2009.07.003)
4. Natural glycol replacement for hair and skin care (https://pdfs.semanticscholar.org/12fb/9e52972759a624a130a8e965dc534b68dccf.pdf)
5. Zemea® Propanediol for Naturally Derived Personal Care Products (Cosmetics & Toiletries, May 2020)
6. Evaluating 1,3-Propanediol for Potential Skin Effects (Cosmetics & Toiletries, May 2013)