There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the Research
Benefits of Skin Toner
- Skin toner can be beneficial when used as part of a comprehensive skin care routine, as it can help improve superficial hydration, deep hydration, skin roughness, mean pore area, melanin heterogeneity, and crow's feet wrinkle depth 1.
- A study found that a guava toner significantly reduced oiliness of the forehead and nose, making it a potential solution for oily skin 2.
- Another study compared the moisturization effects of cream, toner, and spray water, and found that the combination of cream and toner led to the greatest hydration change rate, especially for normal skin 3.
Comparison with Other Skin Care Products
- Moisturizers, including toners, can help restore the integrity of the stratum corneum, reduce transepidermal water loss, and replace skin lipids and other compounds 4.
- The application of cream only was found to be an effective and brief way to achieve favorable moisturization, especially for dry skin, while repeated application of toner can be efficacious for skin hydration 3.
Specific Uses of Skin Toner
- Skin toner can be used to reduce oiliness, as seen in the study on guava toner 2.
- It can also be used to improve skin hydration, especially when combined with cream or other moisturizers 3.
- Additionally, skin toner can be part of a comprehensive skin care routine to improve overall skin health and appearance 1.