A cooling, water-rich plant ingredient with some evidence for healing minor burns. 'Leaf water' is a diluted form that mostly serves as a pleasant base.
Aloe gel from the inner leaf contains polysaccharides (notably acemannan) that hold water and show anti-inflammatory and wound-healing effects in lab studies. Aloe barbadensis leaf water is a watery, diluted form used in place of plain water in a formula; how much active polysaccharide it carries is usually unknown and likely small.
It feels cooling and soothing, which is most of what you notice from an everyday product.
A 2007 meta-analysis of four trials (371 patients) found aloe shortened healing of first- and second-degree burns by about 9 days, but products and methods varied widely. A systematic review of randomized trials found no evidence that aloe prevents radiation skin reactions. Evidence for sunburn relief and everyday cosmetic benefits is weak.
Four controlled trials (371 patients) suggested aloe shortened healing of first- and second-degree burns by about 9 days, but differing products and outcomes limit firm conclusions.
Five published and two unpublished randomized trials gave no evidence that topical aloe vera prevents or reduces radiation-induced skin reactions in cancer patients.