The Ultimate Guide to Skincare Acids: AHAs, BHAs, PHAs & More

Acids are powerful and versatile ingredients in skincare, offering benefits ranging from gentle exfoliation to deep hydration and barrier support. Whether you're looking to smooth texture, brighten your complexion, or target concerns like acne or hyperpigmentation, understanding the different types of acids and how they work is key to making the right choices for your skin.

In this guide, we’ll break down the most common skincare acids—including AHAs, BHAs, and PHAs—explaining their benefits, how to use them, and what to avoid when incorporating them into your routine.

Breaking down the acids

Each type of acid has unique properties that make it suitable for different skin types and concerns. Below, we explore their key functions, benefits, potential side effects, and how to choose the right product for your routine.

• AHA (Alpha Hydroxy Acids) – Refining texture, brightening skin, and boosting hydration by exfoliating the top layer.

• Ascorbic Acid (Vitamin C) – A powerful antioxidant that brightens skin, fades pigmentation, and stimulates collagen for firmer, more resilient skin.

• PHA (Polyhydroxy Acids) – Gentle exfoliation with antioxidant benefits, ideal for reactive and dry skin.

• BHA (Beta Hydroxy Acids) – Penetrating oil, unclogging pores, and targeting acne and congestion.

• LHA (Lipo Hydroxy Acid) – A gentler alternative to BHA, perfect for sensitive, acne-prone skin.

• Azelaic Acid – Soothing, unclogging pores, and evening out skin tone with minimal irritation.

• Hyaluronic Acid – Binding moisture to the skin for deep hydration and a plumper appearance.

• Kojic Acid – Fading dark spots and pigmentation by inhibiting melanin production.

• Ferulic Acid – Boosting the effectiveness of other antioxidants and protecting against free radicals.

• Tranexamic Acid – Targeting stubborn pigmentation and melasma while strengthening the skin barrier.

Protects skin from environmental stressors, brightens pigmentation, and stimulates collagen for firmer, smoother skin.

Ascorbic acid is the purest and most researched form of Vitamin C used in skincare. Unlike exfoliating acids, Vitamin C works as an antioxidant, defending the skin against oxidative stress (pollution, UV exposure, lifestyle factors) and repairing visible damage. It also plays a vital role in collagen synthesis and melanin regulation, making it one of the most effective ingredients for both anti-aging and brightening.

How does it work? Ascorbic acid works by:

• Neutralising free radicals that cause premature aging.
  
• Inhibiting melanin production, helping to fade pigmentation and even out skin tone.
  
• Stimulating collagen synthesis, improving firmness and reducing fine lines.
  
• Boosting other antioxidants such as Vitamin E and Ferulic Acid for amplified protection.
  

Vitamin C is water-soluble, meaning it primarily works in the outer layers of the skin, but its effects reach deep into how the skin behaves and repairs itself.

Proven benefits of Vitamin C include:

• Reducing pigmentation and brightening dull complexions.
  
• Smoothing fine lines and wrinkles.
  
• Repairing photo-damaged skin.
  
• Protecting against oxidative stress from UV and pollution.
  

Side effects: Ascorbic acid may cause stinging or irritation in sensitive skin, especially at concentrations above 15–20%.

Storage & Stability: Ascorbic acid is unstable and oxidises when exposed to light, air, and heat, which reduces its effectiveness. To maximise potency:

• Store in a cool, dark place; refrigeration can extend shelf life.
  
• Use within 3–6 months of opening.

Choosing a product with Vitamin C: Look for serums in opaque, airtight, or dark glass packaging. Concentrations between 10–20% Ascorbic Acid are effective, but if your skin is sensitive, start lower or use a derivative. Products that include stabilisers such as Ferulic Acid and Vitamin E are considered the gold standard for both stability and effectiveness.

Daily SPF use is essential, as Vitamin C does not replace sunscreen but works best alongside it to reduce oxidative stress from UV exposure.

Best suited for:

• Pigmentation and uneven skin tone
  
• Dull, tired skin
  
• Photo-damaged skin
  
• Fine lines and early signs of aging
  
• All skin types, though sensitive skin may prefer derivatives over pure ascorbic acid

Ascorbic acid derivatives are modified forms of Vitamin C designed to be more stable, gentle, and versatile than pure ascorbic acid. These derivatives are less prone to oxidation and can be formulated into a wider range of skincare products. While they are generally less potent than pure Vitamin C, they still deliver strong brightening, antioxidant, and anti-aging benefits with better tolerance for sensitive skin.

How does it work? Vitamin C derivatives must be converted in the skin into active ascorbic acid, which is why their effects can be slower or milder. However, they offer:

• Antioxidant protection against environmental stressors and free radicals.
• Brightening effects, helping to even out skin tone and fade pigmentation.
• Collagen support, improving skin firmness and reducing fine lines.
• Enhanced stability, meaning they resist oxidation and stay effective longer.

Side effects: Because derivatives are gentler, they are usually well-tolerated even by sensitive skin. Irritation is rare, but mild stinging or redness may occur depending on concentration and formulation.

Choosing a product: Look for serums containing well-researched derivatives such as:

• Sodium Ascorbyl Phosphate – acne-friendly, brightening, gentle.
• Magnesium Ascorbyl Phosphate – hydrating, soothing, brightening.
• Ascorbyl Glucoside – stable, good everyday antioxidant.
• Tetrahexyldecyl Ascorbate (THD Ascorbate) – oil-soluble, penetrates deeper, supports collagen.

Products combining Vitamin C derivatives with Vitamin E, Ferulic Acid, or Niacinamide can enhance their effectiveness.

Best suited for:

• Sensitive skin that can’t tolerate pure ascorbic acid
• Beginners looking to introduce Vitamin C
• Pigmentation and uneven skin tone
• Early signs of aging and loss of firmness
• Oily or acne-prone skin (especially with Sodium Ascorbyl Phosphate)

Similar to AHAs, PHAs have a much larger molecular structure which doesn’t let them penetrate as deep and therefore are much less irritating to certain skin types. They also do not sensitise the skin to UV rays.

Most common types of PHAs:

• Glycolactone
• Galactose
• Lactobionic acid

How do they work? PHAs are exfoliants that remove dead skin cells for the surface of the skin. They also fight glycation - this is when a digested sugar molecule attaches itself to collagen within the skin and starts to weaken it and the elastin. PHAs are high in antioxidant activity and also stimulate epidermal growth and repair.

Side effects: Any exfoliating ingredient can cause irritation - remember to gradually add any new skincare ingredient to your routine, even when said to be ”for sensitive skin”. Always wear sun-protection, even when an ingredient claims “not to cause sun sensitivity”.

Choosing a product with PHA: Moisturisers and toners with PHA are a great way to incorporate the ingredient as they usually contain other soothing and moisturising ingredients .

Best suited for:

• Dry, itchy skin
• Sensitive skin with eczema
• Atopic rosacea

Compared to AHA, BHA sinks in deeper into the skin as it is a fat soluble molecule. Fat solubility causes it to reaches the oil in clogged pores and dissolves it along with excess build up. BHA also makes the skin less photo-sensitive as it is shown to absorb UV rays.

How does it work? BHA is an exfoliant that penetrates into pores containing oily sebum and exfoliate dead skin cells within the pores. BHA is a great treatment for people with oily skin or suffering from white heads, blackheads and overall congestion of the skin.

Side effects: As with any skincare ingredient, irritation can occur. BHA is shown to be less irritating than AHAs. When adding a new ingredient to your routine - do it gradually, once a week working your way up to what your skin can tolerate. Salicylic acid is also known to have anti-inflammatory properties because it its derived from acetylsalicylic acid (aspirin).  Due to the fact that BHA absorbs UV rays - this does not mean that you can skip the SPF. SPF should always be applied and especially when exposing the skin to exfoliating ingredients. Other rare but still potential side effects include redness, burning, and scarring. Darker skin types have a higher risk of scaring and developing pigment changes with BHA.

Choosing a product with BHA: Cleansers containing BHA that are left on for 2 minutes have great exfoliating properties with minimal irritation because they are rinsed off. Exfoliating toners are a great way to target specific areas on the skin that may suffer from breakouts, whiteheads and/or blackheads.

In Korean beauty products it is very common to find an ingredient called Betaine Salicylate. It is a combination of salicylic acid and betaine which gives the skin exfoliation and moisture. South Korean formulations are only allowed to contain very small amounts of salicylic acid and therefore betaine salicylate acts as a replacement.

Skincare manufacturers can list BHA in the middle or lower part of ingredients lists as it is effective in lower concentrations (compared with AHAs that work in a higher concentration).

Avoid buying SPF and BHA in one - the ingredients destabilise each other and can cause irritation, unwanted effects and a weaker SPF. A general rule is to always use an SPF last and keep it separate from your other skincare.

Best Suited for:

• Acne
• Blackheads & Whiteheads
• Congested skin
• Oily skin
• Teenage skin

Derived from BHA, it has a similar effect as BHA but a much slower rate of penetration making this an ideal exfoliator for people with extreme sensitivity suffering from acne and congested skin.

It has a higher molecular weight and a stronger lipophilic effect meaning that it dissolves fat, oils and lipids such in pores that may cause breakouts and acne.

How do they work? LHA is a fat soluble exfoliant that dissolves oil. It targets sebum rich sebaceous glands and prevents acne and spots. LHA exfoliation also reduces blockages of dead skin cells within pores and has anti-inflammatory, anti fungal and antibacterial properties. LHA has also been shown to aid the penetration of other skincare ingredients, boosting their effectiveness. LHA has a slow acting time meaning that it can take longer to see results but it is less sensitising to the skin in this way.

Side effects: Even though this is one of the gentler exfoliating acids, some people can over-exfoliate which in turn can cause irritation. Always use an SPF when using exfoliators.

Choosing a product. Spot correctors, area specific products that target the T zone and chin, nose that can get easily congested. As a mask, leave on treatment.

Best suited for:

• Very sensitive skin with acne and breakouts
• Acne, oily skin
• Beginners to acids

This is a gentle exfoliating acid that can be left on the skin with minimal irritation and studies have shown it to prevent and reduce breakouts, fade red marks and pigmentation, smooth out complexion and reduce overall skin sensitivity. It is a dicarboxylic acid that declogs pores and fights inflammation.

How does it work? As a mild, leave on exfoliant its main abilities are to unclog pores and refine skin texture. It slows down the progression of emerging skin conditions which means that it “tells the skin how to behave”. This in turn, decreases swelling, kills acne causing bacteria and decreases keratin production. It takes longer to “work” than your traditional exfoliating acids and therefore results are visible after prolonged use. It is also shown to lighten hyperpigmentation.

Side effects: As with any acid or new ingredient exposed to your skin it can cause a burning sensation, dryness and peeling (depending on concentration used in a formulation). Always remember to use SPF, even though it minimises skin sensitivity, it never protects you from UV radiation.

Choosing a product: Azelaic acid is still relatively new in the cosmetic market. There are prescription ointments and oral tablets but there are great serums emerging that can be incorporated into any skincare routine.

Best suited for:

• Pigmentation
• Rosacea
• Acne and oily skin
• Uneven skin tone

Azelaic acid derivatives are modified versions of azelaic acid created to be more water-soluble, stable, and gentle on the skin. The most common cosmetic derivative is Potassium Azeloyl Diglycinate (PAD, also called Azeloglycin). These compounds deliver many of the same skin-clearing and brightening benefits as azelaic acid, but in a milder and often more hydrating form.

How does it work? While they don’t exfoliate in exactly the same way as pure azelaic acid, derivatives:

• Help regulate sebum production, making them excellent for oily and combination skin.
• Brighten skin tone and reduce redness, hyperpigmentation, and post-acne marks.
• Provide anti-inflammatory benefits, calming sensitivity and irritation.
• Offer added moisturising effects thanks to their glycine component.

Side effects: Because they are milder, azelaic derivatives are generally well-tolerated even by sensitive skin types. Irritation, stinging, or dryness is uncommon but can still occur depending on the formulation. As always, pair with daily SPF to prevent UV damage and pigmentation.

Choosing a product: Look for serums or toners containing Potassium Azeloyl Diglycinate (PAD), usually at concentrations of around 5–6%. These products layer easily into a skincare routine and can be combined with other actives.

Best suited for:

• Sensitive or redness-prone skin
• Oily or combination skin
• Mild acne and clogged pores
• Dull or uneven skin tone

This famous acid has been around for a while and has risen in popularity due to its amazing moisture holding properties. It is not an exfoliant, it is a humectant - it attracts moisture and binds it to the skin. Hyaluronic acid exists naturally in our skin and plays a big part in our skins overall health. High molecular hyaluronic acid hydrates the skin and skin barrier. Low molecular hyaluronic acid hydrates the skin on a slightly deeper level but still works mainly on the top layer of the skin. Low molecular hyaluronic acid has shown to help the skin repair by increasing its self defence.

How does it work? Hyaluronic acid acts like a sponge. It attracts moisture and binds it to the skin and by doing so boosts hydration levels. As hydration is increased, skin cells are happier and can regenerate and repair themselves.

Side effects: Side effects are rare, but like any ingredient - it can cause irritation in some skin. Ultra low molecular hyaluronic acid can cause irritation in some. Another point to remember is that when using hyaluronic acid, it is important to seal it in with a moisturiser as hyaluronic acid alone can evaporate from the skin, drawing out moisture leaving your skin dry and dehydrated.

Choosing a product: Serums are extremely popular and effective. Toners can also add a hydration boost but remember to lock it in with a moisturiser after. Moisturisers containing hyaluronic acid are also available but look for gentle ingredients that are non irritating and do not contain alcohol as this can weaken the hyaluronic acid and cause it to evaporate.

Sodium hyaluronate is a popular ingredient found in many skincare products claiming they contain hyaluronic acid. Sodium hyaluronate is sodium form of hyaluronic acid. They are very similar to each other with the same skin hydrating effects. Sodium hyaluronate is said to be slightly more stable and cheaper for manufacturers so that is why it is seen more on ingredients lists.

Best suited for:

• All skin types
• Dry, dehydrated
• Mature
• Sun damaged
• After being in the sun

Made from different types of fungi and a byproduct of fermented foods from the east, Kojic acid is an tyorsine inhibitor - meaning that it block the amino acid needed to create melanin. It has a lightning effect on the skin and is great for minimising scarring.

How does it work: Tyrosine is an amino acid that creates melanin and kojic acid blocks this synthesis that overtime removes unwanted scarring and brown spots.

Side effects: Kojic acid can cause skin to be more prone to sunburns. It can also cause contact dermatitis in sensitive skin types. Do not use on damaged or broken skin.

Choosing a product: Kojic acid needs to be “left on the skin” to reach its maximum potential so choosing products such as serums, moisturisers and masks are the best way to go. Always follow with and SPF.

Best suited for:

• Pigmentation
• Post acne scarring
• Humid climates

Ferulic acid is a plant-based antioxidant with powerful free-radical fighting abilities. It not only protects the skin from oxidative stress but also enhances the effectiveness of other antioxidants like vitamins A, C, and E. By stabilising vitamin C, it helps maintain potency, supports the skin’s natural defense against UV damage, and reduces inflammation and visible signs of aging such as sagging.

How does it work: Ferulic acid neutralises free radical damage that leads to ageing of the skin and acts as a shield for free radical protection. By doing this, over time it decreases signs of ageing such as fine lines, wrinkles and pigmentation.

Side effects: Certain antioxidants can be “too active” for certain skin types. Remember that any ingredient can cause irritation and ferulic acid has this capability when mixed with fragrance or some preservatives. Remember to add new ingredients into your routine gradually to minimise chances of a reaction. Always use SPF, even though ferulic acid protects against UV rays, it is by no means a sunblock.

Choosing a product: Serums in opaque, dark bottles are the best choice as they have the smaller chance of contamination by heat and light. Look for formulations with minimal ingredients to ensure stability and purity. Use once a day on clean skin followed by a gentle moisturiser. Do not mix ferulic acid with AHA or BHA as this alters the pH and lessens the effectiveness of the antioxidant.

Best suited for:

• All skin types
• Mature skin
• Photodamage and pigmentation 

Tranexamic acid targets stubborn pigmentation and melasma while strengthening the skin barrier. Originally developed in medicine as a derivative of the amino acid lysine to reduce bleeding, it later entered skincare for its impressive ability to fade pigmentation, brown spots, keloid scars, melasma, and pregnancy-related melasma. It also helps decrease skin sensitivity to the sun.

How does it work? Tranexamic acid has powerful anti-inflammatory action where it inhibits tyrosinase synthesis in melanocites. It also blocks the transfer of melanocytes to keratinytes in the top layer of the skin. As melasma is a type of inflammation of the skin, tranexamic acid drastically slows this process.

Equally it helps the skin restore and repair the skin barrier.

Side effects: No documented side effects have been seen yet as this is a relatively new ingredient in the cosmetics industry however as always  - any ingredient can cause irritation so add with caution and care to your routine.

Choosing a product: Serums tend to have the highest potency and can be used as area specific-treatments on the skin. Use once every other day to respect skin tolerance. Tranexamic acid can be combined with retinol, vitamin C, kojic acid to maximise its brightening effect.

Best suited for:

• All skin types
• Dark skin tones prone to keloid scarring
• Acne
• Pigmentation/ sun damage