When it comes to the order of applying skincare products, it is generally recommended to apply products with a lower pH first, followed by those with a higher pH. In the case of snail mucin and BHA (beta hydroxy acid), it is best to apply the BHA product before the snail mucin.

BHA is an exfoliating ingredient that works by penetrating into the pores and removing dead skin cells and excess oil. It has a relatively low pH, typically around 3-4. Applying BHA first allows it to work effectively on the skin and prepare it for the subsequent products.

Snail mucin, on the other hand, is a hydrating and soothing ingredient that can provide moisture and promote skin repair. It generally has a slightly higher pH than BHA. By applying snail mucin after BHA, you can help replenish and soothe the skin after exfoliation.

To summarize, the recommended order of application would be:

1. Cleanse your face.
2. Apply BHA product (follow the instructions on the product for the appropriate amount and wait time).
3. Follow with snail mucin or any other hydrating products.
4. Continue with the rest of your skincare routine, such as moisturizer and sunscreen.

Remember, it's always a good idea to patch test new products and observe how your skin reacts before incorporating them into your regular skincare routine.