Salicylic Acid BHA 4% Serum
Salicylic Acid BHA 4% Serum
Product Description
Product overview
A professional-strength 4% BHA liquid exfoliant serum formulated with Niacinamide and soothing botanical extracts. Designed to deeply unclog pores, reduce breakouts, minimize blackheads, and refine skin texture — all in one lightweight, alcohol-free formula.
Professional-Strength BHA 4%
Twice the concentration of standard BHA serums for deeper pore penetration and more effective exfoliation of dead skin cells and sebum buildup.
Texture & feel
SENSORYProfessional-Strength BHA 4%
Twice the concentration of standard BHA serums for deeper pore penetration and more effective exfoliation of dead skin cells and sebum buildup.
Niacinamide Brightening Boost
Contains Niacinamide (~2%) to help even skin tone, reduce post-acne marks, and regulate sebum production alongside the BHA.
Soothing Botanical Complex
Five botanical extracts including Rose Damascena, Lavender, Green Tea, Lemon Balm, and Mugwort to calm and soothe the skin during exfoliation.
Clean Minimalist Formula
Only 13 ingredients. Free from alcohol, fragrance, parabens, sulfates, silicones, and colorants. Vegan and cruelty-free certified.
Safety & compatibility
SAFEContains 4% Salicylic Acid, which exceeds the 2% maximum recommended by ACOG for use during pregnancy. Choose a lower-concentration BHA product instead.
Topical salicylic acid is generally considered safe during lactation per WHO guidelines. However, 4% is a high concentration — consult your doctor and avoid contact with the baby.
Contains Polysorbate 20, which can feed Malassezia yeast. Not suitable for those managing fungal acne (Malassezia folliculitis).
Very low comedogenic risk. Oil-free formula with no heavy occlusives or pore-clogging ingredients. Safe for acne-prone skin.
4% BHA is a high concentration that can cause irritation, redness, or burning on sensitive or compromised skin. Always perform a patch test under the chin before full-face use.
Free from alcohol, essential oils, fragrance, parabens, sulfates, and silicones. Minimizes risk of sensitization and contact dermatitis.
Ingredient breakdown
INGREDIENTSSalicylic Acid 4%Proven
A beta hydroxy acid (BHA) that is oil-soluble, allowing it to penetrate deep into pores to dissolve sebum plugs, dead skin cells, and debris. It exfoliates both the surface and within the pore lining, making it the gold-standard ingredient for acne and blackhead treatment.
- Mechanism: Oil-soluble exfoliant that penetrates pores to dissolve keratin plugs and sebum buildup
- Research: FDA-recognized acne treatment ingredient at 0.5–2%; concentrations up to 4% used in professional-grade formulations
- Benefits: Anti-inflammatory, antibacterial, unclogs pores, reduces blackheads and whiteheads, smooths skin texture
Niacinamide ~2%Proven
A form of Vitamin B3 that is one of the most well-studied multi-tasking actives in skincare. Stable, effective at various concentrations, and compatible with most other ingredients.
- Sebum regulation: Helps control oil production at 2–5% concentration
- Barrier support: Strengthens the skin barrier by boosting ceramide synthesis
- Brightening: Reduces post-inflammatory hyperpigmentation and evens skin tone
- Anti-aging: Helps minimize the appearance of fine lines and wrinkles over time
Aloe Barbadensis Leaf Extract BaseProven
Used as the primary base of this formula instead of water. Aloe vera provides soothing, moisturizing, and anti-inflammatory properties that help buffer the strength of the 4% BHA, reducing potential irritation.
- Soothing: Contains acemannan and salicylates that calm inflammation
- Hydrating: Acts as a natural humectant to prevent over-drying from the BHA
- Healing: Supports wound healing and reduces redness from active breakouts
Botanical Complex N.O.I.P 72%Promising
A complex of five botanical extracts: Rosa Damascena (Rose), Lavandula Angustifolia (Lavender), Camellia Sinensis (Green Tea), Melissa Officinalis (Lemon Balm), and Artemisia Vulgaris (Mugwort). Together they provide antioxidant, anti-inflammatory, and skin-calming benefits.
- Green Tea (EGCG): Potent antioxidant compounds that protect against free radical damage
- Mugwort: A K-beauty favorite for calming irritated and sensitized skin
- Rose Damascena: Anti-inflammatory and rich in natural phenolic compounds
13 ingredients
Aloe Barbadensis Leaf Extract, Propanediol, Salicylic Acid (4%), 1,2-Hexanediol, Sodium Citrate, Polysorbate 20, Niacinamide, Rosa Damascena Extract, Lavandula Angustifolia Flower Extract, Camellia Sinensis Leaf Extract, Melissa Officinalis Leaf Extract, Artemisia Vulgaris Extract, Hydroxyethylcellulose
Where it fits in your routine
ROUTINEUse 1–3 times per week in the PM. Apply to clean, dry skin. Follow with a hydrating serum and moisturizer. Always apply sunscreen the next morning.
How to use
HOW TO USECleanse Your Face
Start with a gentle, pH-balanced cleanser. Pat skin dry completely — BHA works best on dry skin for optimal penetration.
Apply 2–3 Drops
Using the glass dropper, apply 2–3 drops onto fingertips or a cotton pad. Gently spread over the face, focusing on areas with blackheads, enlarged pores, and active breakouts. Avoid the eye area.
Leave On — No Need to Rinse
This is a leave-on treatment. Allow it to absorb for 1–2 minutes before applying the next step in your routine.
Follow with Moisturizer
Apply a hydrating serum (e.g., hyaluronic acid) and a moisturizer to lock in hydration and counteract any dryness from the BHA.
Sunscreen in the Morning
Always apply SPF 30+ sunscreen the following morning. While salicylic acid itself does not increase photosensitivity, newly exfoliated skin benefits from UV protection.
Who is it for?
WHOPerfect for you if:
- You struggle with persistent blackheads and clogged pores
- You have oily or combination skin with regular breakouts
- You want a stronger BHA beyond the standard 2%
- You prefer minimal, clean ingredient lists
- You want pore-refining and texture-smoothing effects
- You are experienced with chemical exfoliants
Consider alternatives if:
- You are pregnant or planning to become pregnant (4% exceeds recommended limit)
- You have very sensitive or compromised skin barrier
- You are new to chemical exfoliants (start with 0.5–2% BHA first)
- You have fungal acne (contains Polysorbate 20)
- You have dry skin and don't layer with hydrating products
- You need a larger bottle size (this is only 30ml)
Skin type compatibility
SKIN TYPESIdeal match. BHA penetrates oil-filled pores, controls excess sebum, and the lightweight gel absorbs instantly without adding shine.
Works well on oily T-zone areas. Apply targeted to congested zones only and follow with moisturizer on drier cheeks.
High-strength BHA combined with anti-inflammatory botanicals makes this highly effective for breakout-prone skin.
Good for maintenance exfoliation 1–2 times per week to keep pores clear and prevent occasional breakouts.
Can cause dryness and flaking if overused. Use sparingly (once a week) and always layer with a rich moisturizer. May prefer a lower 2% BHA.
4% BHA may be too intense for reactive skin. Patch test required. Consider starting with the 2% version or use as a spot treatment only.
Results timeline
MONTH 3+Initial Purging & Texture Change
Some users experience mild purging (small breakouts) as BHA brings existing clogs to the surface. Skin may feel smoother to the touch. Sebaceous filaments on the nose begin to reduce.
60% noticed smoother textureVisible Pore Reduction & Fewer Breakouts
Blackheads become noticeably less prominent. Active breakouts start clearing faster. Skin appears less oily throughout the day. Redness from existing blemishes begins to fade.
70% noticed fewer breakoutsBrighter, More Refined Complexion
Niacinamide benefits kick in — more even skin tone, reduced post-acne marks, and visible pore minimization. Skin texture feels significantly smoother and clearer.
80% noticed improved skin clarityLong-Term Maintenance Results
With consistent use, skin stays clear with fewer breakouts, refined pores, and a balanced complexion. Many users describe it as a "staple" product at this point.
85% reported it as a repurchase-worthy productRatings by platform
3K+ REVIEWSPros & cons
BALANCEDPraised
- Highly effective at clearing blackheads and clogged pores within 2 weeks
- Affordable price point for a 4% professional-strength BHA
- Clean, minimalist formula with only 13 ingredients
- Absorbs instantly with no greasy or sticky residue
- Aloe vera base soothes while BHA exfoliates
- Fragrance-free, vegan, and cruelty-free
- Multiple repurchase reviews — users describe it as a "staple"
- Effectively reduces sebaceous filaments on the nose
Criticized
- Only 30ml bottle — runs out quickly for full-face application
- 4% is too strong for beginners and sensitive skin types
- Can cause initial purging, dryness, and flaking
- Not pregnancy or fungal acne safe
- Glass dropper application can be slightly messy
- Some users report redness and burning on first use
- Limited availability outside Amazon and iHerb
Budget-friendly alternatives (dupes)
DUPESHalf the BHA concentration (2% vs 4%) but at a fraction of the price. Simpler formula without botanical extracts. Good for beginners or those who find 4% too strong. Slightly thicker, foaming texture.
Uses Betaine Salicylate (4%) — a gentler derivative of salicylic acid. Larger 100ml bottle. Better for sensitive skin but less potent exfoliation than pure salicylic acid. Includes Niacinamide and Willow Bark Water.
Pre-soaked salicylic acid pads at 2% concentration. Convenient pad format but contains menthol which some find irritating. No niacinamide or botanicals. 55 pads per jar for extended use.
Comparison with competitors
SIDE-BY-SIDEStorage & shelf life
12 MONTHS12 months after opening
Store at room temperature in a shaded place away from direct sunlight and heat. Temperature fluctuations during shipping do not affect product stability.
Dark glass dropper bottle — protects active ingredients from light degradation and allows precise application of 2–3 drops per use.
Yes — 30ml is well under the 100ml TSA carry-on limit. Compact glass bottle fits easily in any travel skincare pouch.
Frequently asked questions
FAQThis serum is NOT recommended during pregnancy. It contains 4% Salicylic Acid, which exceeds the 2% maximum concentration recommended by the American College of Obstetricians and Gynecologists (ACOG). High-dose salicylic acid can be harmful during pregnancy. For breastfeeding, topical salicylic acid is generally considered safe according to WHO guidelines since it is poorly absorbed through the skin. However, 4% is a high concentration — consult your healthcare provider before use, and avoid applying to areas that may contact your baby's skin.
No, this serum is NOT fungal acne safe. The formula contains Polysorbate 20, which is a polysorbate ester that can feed Malassezia yeast — the fungus responsible for fungal acne (Malassezia folliculitis). If you are managing fungal acne, look for a BHA product without polysorbates, fatty acids, or esters. The Ordinary Salicylic Acid 2% Solution is a fungal-acne-safe alternative that also contains Polysorbate 20 but in a wash-off context. For a truly FA-safe BHA, consider Stridex pads.
Use caution when combining this serum with other active ingredients. Avoid using retinol, AHA (glycolic or lactic acid), or vitamin C (L-ascorbic acid) in the same routine as 4% BHA — this can over-exfoliate and damage your skin barrier. Instead, alternate: use BHA on some nights and retinol or AHA on other nights. Vitamin C is best used in the morning, while BHA works well in your evening routine. Niacinamide, hyaluronic acid, and ceramides are all safe to layer with this serum.
This serum is best suited for oily, combination, and acne-prone skin types. The 4% BHA concentration is particularly effective at controlling excess oil, unclogging pores, and treating blackheads. It can also work for normal skin as a weekly exfoliation treatment. It is less ideal for dry or very sensitive skin due to the high BHA concentration, which may cause dryness, flaking, or irritation. If you have sensitive skin, start with the brand's 2% version or use this as a spot treatment only.
Most users report smoother skin texture and reduced sebaceous filaments within the first 1–2 weeks of use. Visible improvement in blackheads and breakouts typically occurs by weeks 3–4. The full benefits of niacinamide for skin tone evening and post-acne mark fading take 6–8 weeks of consistent use. Some users experience initial purging (small breakouts) in the first week — this is normal as BHA brings existing clogs to the surface and typically resolves within 2 weeks.
Apply this serum after cleansing and toning, but before heavier serums and moisturizer. The ideal routine order is: Cleanser → Toner → This BHA Serum → Hydrating Serum (e.g., hyaluronic acid) → Moisturizer → Sunscreen (AM only). Use 1–3 times per week in the evening. Apply to clean, completely dry skin for best penetration. A couple of drops is enough for the whole face — no need to drench a cotton pad.
No — this serum has a very low comedogenic rating of 1/5. The oil-free formula contains no heavy occlusives, mineral oil, silicones, or known pore-clogging ingredients. In fact, salicylic acid actively works to unclog pores by dissolving the dead skin and oil that cause comedones. The lightweight gel formula absorbs instantly without leaving any residue that could contribute to clogged pores.
The serum has a Period After Opening (PAO) of 12 months. At the recommended usage of 2–3 drops, 1–3 times per week, the 30ml bottle typically lasts 2–3 months. Store at room temperature away from direct sunlight. The dark glass bottle helps protect the active ingredients from light degradation. If the serum changes color significantly, develops an unusual odor, or separates, discontinue use.
Verdict: The Cos De BAHA Salicylic Acid BHA 4% Serum is a potent, no-nonsense exfoliating treatment that delivers on its promises. Its professional-strength 4% BHA paired with Niacinamide and a soothing botanical complex makes it one of the most effective and affordable options for stubborn blackheads, clogged pores, and acne-prone skin. The ultra-clean 13-ingredient formula is a standout in a market full of unnecessarily complex products. However, the high concentration means it is not suitable for everyone — BHA beginners, pregnant women, and those with fungal acne should look elsewhere. The small 30ml bottle is also a drawback for regular full-face users. Overall, if you have oily or acne-prone skin and want a powerful BHA at a K-beauty-friendly price, this serum is an excellent choice that has earned its cult following.
Product Overview
Quick product notes are a great way to check if a product is free from commonly avoided ingredients by skincare enthusiasts. These preferences come about for different reasons depending on the ingredient such as personal experiences, sensitivities, health preferences & etc.
Just because a product is not free from a common preference does not mean it's a bad product! You can make a personal decision whether or not you want to use a product that contains these ingredients or not - click the labels of the preference to read more about them.
Quick Product Notes
Ever used a product that promised a certain effect but provided no results? It might not have contained any notable ingredients that could have been responsible for that promised effect. It doesn't matter what the marketing or packaging «promises» it can do, if it doesn't contain anything that can help - then the likelihood of it helping is low.
We help you identify key notable ingredients that have been shown to help with effects such as acne-fighting, brightening, UV-protection, wound healing & anti-aging to help you achieve your skincare goals smarter. Please note that different notable ingredients have varying levels of research behind them, some are extremely well proven yet some have mixed research in their efficacy.
Just because a product doesn't contain any notable ingredients doesn't mean it's bad. And a product with notable ingredients (or even many) doesn't necessarily guarantee the efficacy of the product performing these effects either. There are other factors such as ingredient quality, concentration and formulation that will ultimately determine this.
Be smart and use this as just a starting point for you to make more informed and smarter choices and compare it with reviews to see if the product is right for you
Notable Effects & Ingredients
Why are some products great for some people and horrible for others? Well everyone has different skin types and different reactions to the same ingredients.
We've identified a range of ingredients that are commonly regarded as potentially good or bad for those with Dry, Oily/Acne-Prone or Sensitive skin.
A product that contains good or bad ingredients for your skin type doesn't always flat out make the entire product good or bad for your skin. There are other factors such as ingredient quality, concentration and formulation that will ultimately determine your skins reaction.
One of the best ways to use this section is to troubleshoot products you've had bad experiences with in the past. Check if it contains any of the marked ingredients to point out suspect ingredients to avoid in the future!
Ingredients Related to Skin Types
Ingredient Safety Breakdown refers to the percentage % of ingredients in different risk categories as classified by EWG (Environment Working Group) if they are available. There are almost endless cosmetic ingredients and they are one of the few organisations globally that have assigned ratings to a lot of the more commonly used ingredients which is why we reference them.
EWG is seen by many to be more on the alarmist side in their assignment of health ratings resulting in rating ingredients as riskier than they actually are. We recommend using this a reference point rather than a strict guide of ingredient safety and to always do further research if into ingredients that you may find suspect.
Ingredient Safety Breakdown
Product ingredient list
| EWG | CIR | Ingredient Name & Cosmetic Functions | Notes |
|---|---|---|---|
| 0 |
Aloe Barbadensis Leaf Extract
Emollient, Humectant, Skin Conditioning
|
Hydrating
Redness
Irritation
|
|
| 1 |
Propanediol
Solvent, Viscosity Controlling, Viscosity Decreasing Agent
|
|
|
| 4 |
Salicylic Acid
Skin Conditioning, Masking, Fragrance, Hair Conditioning, Antidandruff Agent, Antiacne Agent, Denaturant, Preservative, Exfoliant, Keratolytic, Corn/Callus/Wart Remover
|
Pores
|
|
| 1 |
1,2-Hexanediol
Solvent, Skin Conditioning
|
Hydrating
|
|
| 1 |
Sodium Citrate
Masking, Ph Adjuster, Buffering Agent, Chelating
|
|






