There are a few different types and the age of the plant will affect what it has on-board. But most will contain a generous amount of polysaccharides and fatty acids - which is partly why it is a good choice as an anti-inflammatory and can improve wound-healing. It also contains saponins, that give it that slightly soapy quantity, and help make it a very good cleanser - with added anti-inflammatory effect, without drying skin. It is also a natural source of salicylic acid, which is often used to help several skin conditions, including acne.
You do ask specifically for skin benefits, but just incase other people are intent on swallowing it - do be careful. If you slice a leaf/branch you will see the typical, clear gel, with a slight greenish tinge. There is also an orange coloured liquid part - called the latex; this is a strong laxative. It is important to stand the branch on the cut end (it’s not going to balance on the other end…) and wait for all the orange gloop to leak out. Only when it is washed out completely, should you then start to remove the flesh for eating. (You don’t want the latex on your skin either, so remove it, wherever you are putting the aloe.)
Overall, I think it is a great plant, I grow many. Unfortunately the aloe used in skincare is very unlikely to be fresh - every ingredient used must pass quality control tests to ensure its stability and safety. These include: pH and microbial analysis, and stability testing over time to assess its effectiveness. Very few, if any, brands will be chopping up fresh aloe and using it, as the flesh of each plant will need to have been approved for use - which takes months and by then, it’s certainly not nice fresh aloe. You can buy it, but don’t be fooled by the bottle of glycerine that contained a small percentage of aloe juice. Even the actual gel won’t be sold by reputable suppliers without a preservative. So if you are inclined to use the fresh plant, grow one yourself.
Having said that, it does retain its properties well, especially when freeze-dried and used re-constituted, from a powder and it has remained a staple in skincare because it is such an effective, generally safe ingredient.