How do you start an AHA or BHA without irritation?

Start one acid at a time, patch test it first, and use it only a few nights a week. The Ordinary suggests that people new to exfoliating acids start 2 to 3 times a week and increase gradually [1]. Follow with moisturizer [4] and wear sunscreen every morning [2][3]. Corneo starts an acid at 2 nights a week.

Pick one acid

AHAs and BHAs are both chemical exfoliants.

• AHAs. Glycolic and lactic acid are the most common in cosmetics [2].
• BHAs. Salicylic acid is the most common BHA in cosmetics [3].

Strength matters. The FDA reports that an expert panel found glycolic and lactic acid products safe for consumers at 10% or less, with a pH of 3.5 or higher, when they protect from sun sensitivity or carry sun directions [2].

Add only one new product at a time. The AAD advises starting with one product, because several new products at once can irritate skin [5].

Patch test first

The FDA suggests testing any BHA product on a small area of skin before using it on a large area [3]. The Ordinary advises a patch test before using its glycolic acid toner [1]. Its method: apply a small amount to the upper forearm, keep it dry, and rinse after 24 hours [1]. If you see redness, burning, itching, blistering or irritation at any point, do not use the product [1].

Corneo’s schedule for a new acid

This is Corneo’s pacing, not a prescription.

The weeks are approximate. Missed nights do not count toward the next step. The AAD adds that the more aggressive the exfoliation, the less often it needs to be done [4]. Your product’s label comes first: the FDA advises not using a BHA product more often than the label directs [3].

What an acid night looks like

1. Wash with a gentle cleanser.
2. Apply the acid. The AAD says never to exfoliate over cuts, wounds or sunburned skin [4].
3. Apply moisturizer right after exfoliating, as the AAD advises [4].
4. The next morning, use sunscreen.

Keep other strong actives off acid nights. The Ordinary says not to use its glycolic acid toner with other direct acids, such as salicylic acid, or strong retinoids in the same routine [1]. Retinol with AHA or BHA covers how to fit both into one week.

Sunscreen is part of starting

The FDA found that four weeks of AHA use raised sensitivity to UV reddening by 18 percent [2]. Its suggested label says to use sunscreen, wear protective clothing and limit sun exposure while using the product and for a week afterward [2]. For BHAs, the FDA advises sun protection too [3].

When to step back

• Stinging, burning or tingling. The AAD says to stop a product that stings, burns or tingles, because it is irritating your skin [5]. For BHAs, the FDA says to stop on irritation or prolonged stinging [3].
• Redness after exfoliating. The AAD warns that over-exfoliating can cause redness and irritation [4].
• Sensitive or peeling skin. The Ordinary does not recommend its glycolic toner on sensitive, peeling or compromised skin [1].

Corneo offers to step you down a level after stinging or peeling. It never changes the schedule by itself.

Skin type and tone matter too. For dry or sensitive skin, the AAD suggests a washcloth and a mild chemical exfoliant [4]. It also says aggressive exfoliation on darker skin tones may lead to dark spots [4].

What Corneo does

Corneo paces an acid on this schedule, from 2 nights a week, and steps up only after the nights were done and your skin is settled. It never puts an acid on the same night as a retinoid, and it offers a step down on stinging or peeling. Check an acid against retinol or audit your whole shelf.

FAQ

Should I start with an AHA or a BHA?

The sources here give the same starting advice for both: one product, a patch test, sunscreen and a slow start [1][3][5]. Pick the one that suits your skin and follow its label [3].

Can I use an acid in the morning?

The Ordinary suggests its glycolic toner in the evening [1]. AHAs raise sun sensitivity [2], so a morning acid needs sunscreen.

Can I use two acids?

The Ordinary says not to use its glycolic toner with other direct acids, such as salicylic acid, in the same routine [1]. Start one, and add another only after the first is settled.