From pore-cleaning salicylic acid to line-smoothing retinol, some of the most effective ingredients in our skin-care routines are acids. Used excessively or incorrectly, however, acids can also cause irritation, redness, and inflammation, which means if you've got sensitive skin, chances are you've probably ruled them off already. While it might sound completely counterintuitive, incorporating acids into your skin-care regimen could actually improve skin sensitivities over time. Understanding which ingredients to choose, how frequently to use them, and, more specifically, the formula best suited for your sensitivity, tends to be where the confusion lies. To find out more, we spoke to leading dermatologists about how to incorporate acids into your routine safely and effectively, as well as the best formulas designed specifically for sensitive skin. Understanding the Cause of Sensitive Skin Is the First Step First and foremost, it's really important to understand what's causing your skin sensitivity. "It's still possible to use acids if you have sensitive skin, but you'll need to understand why your skin is like that in the first place," Ifeoma Ejikeme, skin expert and medical director of Adonia Medical Clinic, told POPSUGAR. "Sensitivity can be caused by using strong active ingredients too quickly or the wrong products for your skin type, or by factors like extreme dryness, certain medications, allergies, and even certain medical conditions such as rosacea," all of which can impact our skin barrier function and consequently cause irritation when using acids thereafter. Knowing why your skin is sensitive and treating that first will not only improve that sensitivity, but it also means that the acids you use afterwards will work effectively and without irritating your skin. For instance, if you have extremely dry skin, Dr. Ejikeme explained that it's important to restore hydration levels first, before adding lactic acid - a gentler alpha hydroxy acid (AHA) exfoliant - once a week. Alternatively, your skin might actually be sensitive due to rosacea or eczema, which compromises our skin's barrier function (the outermost protective layer of the skin which helps to shield and prevent moisture loss) and can lead to flakey, irritated skin. Without restoring the skin barrier function and looking at the root of the issue, it could lead to further irritation, dryness, and inflammation if you start using acids. If you have rosacea, eczema, or sensitized skin, you need to repair your skin's barrier function before adding acids into your routine. To do that, you need to start incorporating ingredients such as hyaluronic acid (which is not an exfoliating acid like glycolic or lactic), ceramides, niacinamide, glycerin, and panthenol. Dr. Ejikeme recommended the entire CeraVe skin-care range for this, which combines three essentials ceramides to protect the skin's barrier alongside hyaluronic acid. Once you've worked on treating sensitized skin and restoring the skin barrier, choosing an acid depends on your main skin goal: brightening (glycolic acid), spot clearing (also glycolic acid), hydrating (lactic acid), acne (salicylic acid), redness (azelaic acid), and so on. The Best Acids to Use If You Have Sensitive Skin "There is a common myth that acids shouldn't be used on sensitive skin," Robert Murad, MD, board-certified dermatologist and founder of Murad Skincare, told POPSUGAR. "However, there are actually some [acids] that can help improve sensitive skin's resilience and strengthen the barrier, even reducing redness over time." For example, Dr. Murad recommended a variety of different acids, which are all suitable for sensitive skin: "Lactic acid, due to its skin-conditioning benefits and ability to enhance hydration; azelaic acid, which is antimicrobial and anti-inflammatory and often used to treat the redness associated with rosacea; and salicylic acid, which is often used for redness and inflammation and, when combined with other soothing ingredients, acts as an anti-inflammatory." When it comes to lactic and glycolic acid, while both AHAs offer exfoliating results, lactic acid tends to be the gentler option of the two, as it has a larger molecule size, meaning it exfoliates on a surface level and hydrates the top layer of skin. Glycolic acid, on the other hand, has a smaller molecule size and can penetrate deeper into the skin to remove dead skin cells and unclog pores. "Many people shy away from glycolic acid as it is often thought too harsh for sensitive skin, but it can benefit these skin types by opening up hydration pathways, stimulating collagen and elastin production, and helping to strengthen the skin barrier over time," Dr. Murad said. "The key is to use serums that combine glycolic acid with soothing ingredients and hydrators that are created to help sensitive skin types, like the Murad Hydro-Dynamic Quenching Essence (£70)," which combines ingredients like hyaluronic acid, lentils, and watermelon to boost hydration and avoid irritation. Dr. Ejikeme, however, advised that you should only be using glycolic acid if your skin barrier is at its optimum health, and only ever at 10 percent (the highest percentage you'll see over the counter is 30 percent). Mandelic acid, another form of AHA, is another option for sensitive skin types according to Dr. Ejikeme. Like lactic acid, mandelic acid has a larger molecule size (meaning it's more gentle on the skin), which helps treat acne, regulate sebum production, and help decrease breakouts over time. "For sensitive skin, mandelic acid is my top choice," Ife J Rodney, MD, founding director of Eternal Dermatology + Aesthetics in Columbia, said. "Because the mandelic acid molecule is larger than other AHAs', it penetrates the skin slowly and causes less irritation." Even more user friendly perhaps are polyhydroxy acids, or PHAs, which, as Shereene Idriss, MD, board-certified cosmetic dermatologist based in New York City, confirmed, are starting to make their way into skin-care formulations more and more: "Polyhydroxy acids are finally getting a spot in the limelight [after] long having been overshadowed by their BHA and AHA counterparts" she told POPSUGAR. "Unlike AHAs and BHAs, which are smaller, PHAs are bigger and therefore cannot penetrate as deep into the skin. They work by sloughing off the most superficial layer of skin, helping with textural issues, fine lines, and brown spots without being as irritating, so they are ideal for those with sensitive skin." These chemical exfoliants are also rich in antioxidants and anti-inflammatory properties that help make them suitable for skin sensitivities like rosacea and eczema. Better yet, PHAs are humectants, which means they attract water molecules and hydrate your skin in the process as a result. From Medik 8 to The Inkey List, brands are following suit to reap the benefits of this gentler acid, with the name cropping up in everything from toners to serums. It's thought to be best used, however, in products that are left on the skin (like your daily moisturizer or serum), as this gives more time to loosen the skin cells and remove surface-level impurities from the skin more effectively for a smoother, more even skin tone. Using Retinol If You have Sensitive Skin (Because Yes, It's an Acid) Loved in the industry for its line-smoothing, tone-improving, and acne-fighting properties, retinol is the gold standard when it comes to skin-care ingredients. However, the it's also associated with causing dryness and irritation. Dr. Ejikeme recommended that if you're trying retinol for the first time and you have very sensitive skin, to look for retinaldehyde instead. A little science lesson before we continue: retinoic acid (which is an acid, obviously) is the only retinoid that your skin can actually use, but it's also only available with a prescription. Other retinoids you may have heard about - retinol, retinaldehyde, retinyl palmitate - are also vitamin A derivates, however they have to undergo a conversion process in order to turn into retinoic acid before your skin can utilize the ingredient. Retinaldehyde (which you'll often see as "retinal" on an INCI list), is basically one step away from being retinoic acid. If you use it at 0.025 or 0.5 percent, according to Dr. Ejikeme, it will still offer the skin-improving results synonymous with retinoic acid, whilst being gentler on sensitive skin types. If you've never tried retinol before, Dr. Ejikeme recommended using retinaldehyde twice a week, followed by a hydrating moisturizer applied on top, and SPF the next morning (and every morning, mind you); then increase by a day each week to build up resilience. How to Incorporate Acids Into Your Current Skin-Care Routine When you think about your morning and evening skin-care routine, you've probably already acquired quite a few extensive steps (cleanse, tone, moisturize, and so on), therefore, knowing exactly when to use acids and how frequently is a major part of the puzzle. The rule of thumb is to always start slowly and proceed with caution: test the acid on a small patch of skin before you use it on your entire face to avoid irritation and see if any sensitivity occurs. Incorporate one acid first before adding another, and if you are able to, try and "have a consultation to ensure you are choosing the acids that are right for your type of sensitivity," said Dr. Murad. He recommended that including an acid in your cleansing routine is a good starting point for anyone who hasn't tried at-home acids before. Understanding the Strength of Acids These days, trying to decipher the ingredients, percentages, and numbers cropping up in your daily moisturizer, cleansers, and serums can feel overwhelming. It's important to remember a few key things. Firstly, while we know that different acids target different skin-care concerns, their strength depends on the molecular size of the acid. As mentioned, azelaic, mandelic, and polyhydroxy acids are better suited to sensitive skin because they are made up of a larger-sized molecule, which means they the penetrate the skin more slowly and therefore provide gentler results helping to calm inflammation in the skin. Glycolic acid, on the other hand, has a smaller molecule that travels deeper into the skin and can cause reactions and inflammation if used incorrectly. Secondly, as Dr. Ejikeme pointed out, all acids have different and unique percentages which can be confusing, as a high percentage may not always mean the formula is super strong. For instance, you can't purchase salicylic acid at more than 2 percent over the counter or in store, lactic acid at more than 10 percent, retinol can't be more than 2 percent, and glycolic acid is capped around 30 percent. So, instead, look for the lowest percentage of the acid you've chosen and one that's pH-balanced to build up your resilience before moving to a higher percentage - like starting with a low 5 percent lactic acid or 0.025 percent retinol. "Studies have shown that lower levels of acids combined with anti-inflammatories and hydrators offer the best results and longer term benefits," Dr. Murad said. "This is because high percentages can often cause inflammation, peeling, and irritation, compromising the moisture barrier which can lead to excessive dryness and even hyperpigmentation." It's also a good idea to look out for other ingredients combined with acids, such as encapsulated hyaluronic acid, antioxidants, and soothing ingredients like pomegranate, licorice root, and niacinamide, said Dr. Murad, all of which can help calm skin and strengthen the protective barrier. For more of the best acid-based skin care for sensitive skin and specific concerns, check out the gallery ahead.