Toner has had a bit of an iffy reputation in its history. I blame the 20th century for this, pushing astingent and drying toners that were a bit like sweeping a Lysol wipe over your face post-cleanse (very Howard Hughes energy).
But if you ask K-Beauty evangelists, toner is must must must. But that's because toner is an essential hydrating step that helps your entire skincare routine work better. If you love makeup primer, toner is basically your skincare's primer. Think of it that way.
What is toner?
The purpose of toner is to prep your skin to absorb treatments, kind of like how a sponge can't work properly dry; it has to be damp otherwise it's just like a hard, stiff potato chip that doesn't lather up at all. Your skin has to be a bit damp for it to absorb your treatments fully.
When to use toner
Now how you apply it is up to you. You can splash some in the palm of your hand and pat it onto your face, Home Alone-style. You can splash some onto a cotton pad and sweep it across your face (I like doing this after cleansing a full face of makeup to grab any leftover makeup or oil residue leftover). Some toners come in a spray, which is also easy-peasy. The point is to moisten your face, not necessarily rub your skin raw, you know?
Nowadays, skincare is booming, and toners have grown and expanded quite a bit, but not so much its understanding. So, here's a little primer on the post-cleanser step.
Types of toners
These are gentle formulas that are meant to put more water back into your skin. They usually boast hyaluronic acid, glycerin, and other hydrators as their top ingredients. For dry, dehydrated, or even "normal" skin types, a hydrating toner really does the most. By adding more hydration into your skin, it makes your skin look and feel way more cushiony and dewy, ready to absorb whatever serums you may have in mind and moisturizer for an overall way more hydrated look and feel to your skin.
Toners with active ingredients will usually include some form of chemical exfoliants, like lactic acid, mandelic acid, AHAs, BHAs, or PHAs. These can be hydrating as well, but the main purpose is to gently exfoliate, which helps loosen dead skin cells so your serums and moisturizers can penetrate more easily. Active toners can also contain pre- or probiotics or enzymes. If you use an exfoliating toner, you won't need to double-up with serums that also contain similar actives (that could easily become overkill and lead to irritation). In general, you shouldn't combine actives, and tbh I only use my active toners at night when I don't have to worry about increased sunlight sensitivity. You totally can use them in the morning but you cannot (cannot!) forget SPF after that.
The ol' classic — these usually contain witch hazel and sometimes alcohol, which can be majorly drying for skin. Astringent toners are usually marketed towards oily skin types as a means to sop up excess sebum and oil and tighten pores, but truthfully this can backfire and cause your skin to produce MORE sebum because you're removing too much of it. These toners can sweep up excess residue that you didn't properly cleanse, but it's not toner's job to pick up your cleanser's slack, so you may want to either cleanse longer and more thoroughly or find a better cleanser.