Exfoliation | January 29 2025

Different types of acid in skincare and when to use them

Acids have become key ingredients in modern skincare, and they offer a range of benefits, from exfoliation and hydration to brightening and anti-aging. As research into skincare science has evolved, new types of acids have joined the market, each with distinct properties that target specific skin conditions and needs. 

Choosing the right acid for your needs can transform your skin. In this guide, we’ll explore the types of acids and how to incorporate them into your routine. 

Alpha hydroxy acids (AHAs)

Alpha hydroxy acids, or AHAs, are water-soluble acids derived from natural sources such as fruits, milk, and sugar cane. When it comes to what AHAs do for the skin, their primary role is to work on the skin’s surface, exfoliating and removing dead skin cells to leave skin looking smoother and more radiant. 

By exfoliating the skin’s outermost layer, they’re suited to brightening, improving texture, and minimizing the appearance of fine lines.

Types of AHAs

• Glycolic acid: Derived from sugar cane, this acid is an effective exfoliant due to its small molecular size, allowing it to deeply penetrate skin. This makes it ideal for tackling the appearance of wrinkles, uneven texture, and discoloration. Glycolic acid is suited for normal to combination skin types but may be too strong for sensitive skin.
• Lactic acid: This is derived from lactose – a carbohydrate found in milk. With its larger molecular size, it is gentler than glycolic acid as it doesn't penetrate as deeply. It hydrates while exfoliating, making it suitable for sensitive or dry skin types. Lactic acid can soften rough patches and improve skin’s overall smoothness without irritation.
• Mandelic acid: This AHA is even gentler than lactic acid, as it has an even larger molecular structure, which reduces the likelihood of irritation due to its slow penetration. 

How to use AHAs

Each alpha hydroxy acid has different percentage strengths. Those who are new to using these should start with the lowest percentage and gradually build up as their skin becomes more tolerant. 

Incorporate AHAs into your evening routine 2-3 times per week, gradually increasing as your skin builds tolerance. Avoid mixing them with other strong exfoliants or acids to protect the skin barrier. After applying AHAs, follow up with a hydrating moisturizer, and always use SPF the next morning, as AHAs can increase sun sensitivity.

Beta hydroxy acids (BHAs)

Beta hydroxy acids (BHAs) are oil-soluble, meaning they can penetrate deeper into pores than AHAs. This makes BHAs especially effective for oily, blemish-prone, or combination skin types, as they can help to clear pore congestion and reduce excess sebum.

Salicylic acid is the most widely used BHA. Its benefits are that it can deeply cleanse pores, reduce blackheads, and treat mild blemish, making it a popular choice. It works by exfoliating the inside walls of pores, which prevents clogging and reduces breakouts.

How to use BHAs

As they are typically gentler than AHAs, BHAs are generally suitable for daily use. However, like AHAs, these come in different percentage strengths and how often you use them depends on your skin’s tolerance. 

BHAs often feature in toners, serums, or cleansers. When it comes to how to use BHAs like salicylic acid for the first time, try applying a salicylic acid-based toner after cleansing – either in the morning or at night – followed by a hydrating moisturizer. Avoid using it with other acids to minimize irritation. As BHAs can increase skin sensitivity to the sun, when using products containing these in the morning always follow up with an SPF to protect your skin.

Polyhydroxy acids (PHAs)

Polyhydroxy acids, or PHAs, are the gentlest exfoliating acids. They have a larger molecular structure, which means they penetrate the skin less deeply, providing mild exfoliation with minimal irritation. 

PHAs are suited to individuals with sensitive, rosacea-prone, or dry skin that can't tolerate stronger acids. They often feature in products that target sensitive skin, such as those in the ZO® Sensitive Skin range.

Types of PHAs

• Gluconolactone: This PHA is effective for exfoliating sensitive skin, helping to improve texture and smoothness over time without irritation. It shares similarities with AHAs, but due to its larger molecular structure, it can't penetrate the skin in the way AHAs can, reducing the possibility of irritation. 
• Lactobionic acid: Known for its antioxidant properties, lactobionic acid not only provides gentle exfoliation but also hydrates the skin and helps improve elasticity.

How to use PHAs

PHAs are generally used 2-4 times per week in the evening, although their gentle nature means they can often be used more frequently if your skin can tolerate this acid. While they're milder than AHAs and BHAs, an SPF is still recommended during the day when using products containing polyhydroxy acids.

Hyaluronic acid

Hyaluronic acid is a humectant, meaning it attracts and retains moisture in the skin. Unlike other acids we've covered so far, it doesn't have exfoliating properties. Instead, it hydrates by drawing water from the environment into the skin, making it essential for maintaining a plump, smooth, and hydrated complexion. Hyaluronic acid is suitable for all complexions, especially those with dry or dehydrated skin.

It is effective for keeping the skin hydrated, soft, and resilient. Its ability to retain up to 1,000 times its weight in water makes it excellent for locking in moisture, especially in dry or cold climates where skin tends to lose hydration. 

How to use hyaluronic acid

Hyaluronic acid can be used both morning and evening. Apply it in small layers after cleansing but before heavier creams or oils to maximize hydration. For best results, apply it to damp skin to help lock in moisture. Hyaluronic acid pairs well with nearly all other skincare ingredients and is often found in serums, moisturizers, and eye creams. 

Ascorbic acid (vitamin C)

Ascorbic acid, or vitamin C, is good for your skin if it's dull, discolored, or sun-damaged. It's a powerful antioxidant that protects your skin from environmental damage and brightens the complexion. It also reduces signs of aging, such as dark spots and discoloration. In addition, this acid boosts collagen production, helping to maintain skin elasticity.

Another benefit of vitamin C is that it helps to neutralize free radicals in the environment such as UV rays, pollution, and other damaging environmental factors. By introducing vitamin C-based products into your routine, you will see a brighter, more even complexion.

How to use ascorbic acid

Apply vitamin C once or twice a day. Start by applying in the morning after cleansing but before adding sunscreen. 

Vitamin C can sometimes cause mild tingling, especially if you’re new to using it, so start with a lower concentration if you have sensitive skin. Vitamin C can be layered with other antioxidants but should not be mixed directly with AHAs or BHAs due to the potential for irritation.

Introduce acids to your skincare regimen with ZO®

If you want to introduce acids to your skincare routine, we can help. Begin by building your ZO® regimen using our Regimen Finder. This will help you discover the best acids for your needs. 

From there, you can ask us questions or get tips and advice about our products. Get in touch with our friendly team of ZO® Skin Health experts and we'll provide information and advice about ingredients that can match your requirements.