BETA HYDROXY ACIDS (BHAs)

Beta Hydroxy Acids (BHAs) are a class of organic carboxylic acids characterized by a hydroxyl group positioned on the beta carbon (the second carbon atom from the carboxylic acid group), making them structurally and functionally distinct from alpha hydroxy acids (AHAs).
Beta Hydroxy Acids (BHAs) are oil-soluble (lipophilic) compounds, which allows them to penetrate through sebum-filled pores and exfoliate from within, making them uniquely effective for oily, acne-prone, and congested skin types.
Beta Hydroxy Acids (BHAs) function primarily as chemical exfoliants, keratolytic agents, and anti-inflammatory compounds, and are widely used in cosmetic, pharmaceutical, and dermatological applications.

CAS Number (Salicylic Acid, primary BHA): 69-72-7
EC Number (Salicylic Acid): 200-712-3
Molecular Formula (Salicylic Acid): C7H6O3
Molecular Weight (Salicylic Acid): 138.12 g/mol
E Number: Not applicable (cosmetic/pharmaceutical ingredient, not a food additive)
INCI Name: Salicylic Acid (primary BHA); Betaine Salicylate; Beta-Hydroxybutanoic Acid

Synonyms: BHA, BHAs, Beta Hydroxy Acid, Beta-Hydroxy Acid, Salicylic Acid, 2-Hydroxybenzoic Acid, Orthohydroxybenzoic Acid, Salicylate, Betaine Salicylate, Beta-Hydroxybutanoic Acid, Beta Hydroxybutyric Acid, Trethocanic Acid, Capryloyl Salicylic Acid, Willow Bark Extract, Oil-Soluble Exfoliant, Lipophilic Hydroxy Acid, BHA Exfoliant

Beta Hydroxy Acids (BHAs) belong to the broader category of hydroxy acids alongside alpha hydroxy acids (AHAs) and polyhydroxy acids (PHAs); the key structural difference is the position of the hydroxyl group relative to the carboxylic acid group, with BHAs carrying the hydroxyl on the beta carbon.
Beta Hydroxy Acids (BHAs) are oil-soluble rather than water-soluble, a defining property that enables them to dissolve in and penetrate through the lipid-rich sebum that fills follicles and pores, allowing exfoliation to occur at the source of congestion rather than only at the skin surface.

The most widely used Beta Hydroxy Acid (BHA) in skincare and pharmaceutical formulations is salicylic acid (2-hydroxybenzoic acid, CAS 69-72-7), originally derived from willow bark (Salix alba) and meadowsweet plant extracts, though modern production relies predominantly on synthetic synthesis for consistency and stability.
Beta Hydroxy Acids (BHAs) are used in over-the-counter and prescription products at concentrations of 0.5 to 2% for daily use and at higher concentrations of up to 30% in professional chemical peel formulations under supervised dermatological care.

Beta Hydroxy Acids (BHAs) require a formulation pH below 4.5 to remain in their un-ionized, membrane-permeable form; above this pH threshold, the acid becomes ionized and loses its ability to penetrate the follicle regardless of the stated concentration.
Beta Hydroxy Acids (BHAs) are recognized and regulated by the US FDA as active drug ingredients for over-the-counter acne treatment at 0.5 to 2%, and are included in the EU Cosmetics Regulation (EC) No 1223/2009 with specific concentration and labeling requirements.

Uses of Beta Hydroxy Acids (BHAs):
Beta Hydroxy Acids (BHAs) are used as chemical exfoliants in cleansers, toners, serums, moisturizers, face masks, and leave-on treatments designed to remove dead skin cells, unclog pores, and smooth skin texture.
Beta Hydroxy Acids (BHAs) are used in acne treatment formulations to dissolve the sebum and cellular debris inside blocked follicles, reducing blackheads, whiteheads, and inflammatory acne lesions.

Beta Hydroxy Acids (BHAs) are used in anti-aging skincare products to promote cellular turnover, improve skin tone and texture, reduce the appearance of fine lines and wrinkles, and enhance the penetration of other active ingredients by removing the barrier of dead surface cells.
Beta Hydroxy Acids (BHAs) are used in chemical peel treatments in professional and clinical settings at concentrations ranging from 20 to 30% to achieve deeper exfoliation and address photoaging, hyperpigmentation, acne scarring, and uneven skin tone.

Beta Hydroxy Acids (BHAs) are used in pharmaceutical formulations as keratolytic agents for the treatment of dermatological conditions including psoriasis, seborrheic dermatitis, dandruff, warts, calluses, corns, and hyperkeratotic skin disorders.
Beta Hydroxy Acids (BHAs) are used in antifungal and antibacterial topical preparations, exploiting the antimicrobial properties of salicylic acid against bacteria and fungi involved in skin infections and dandruff.

Beta Hydroxy Acids (BHAs) are used in hair and scalp care products including anti-dandruff shampoos and scalp treatments, where salicylic acid acts as a keratolytic to loosen and remove scalp buildup and flaking.
Beta Hydroxy Acids (BHAs) are used in foot care products including callus removers, corn plasters, and foot creams at higher concentrations of 10 to 40% to soften and remove thickened, hyperkeratotic skin.

Beta Hydroxy Acids (BHAs) are used in combination products formulated with AHAs, retinol, niacinamide, and vitamin C to deliver complementary exfoliating, brightening, and anti-aging benefits.
Beta Hydroxy Acids (BHAs) are used in body care formulations including body washes and lotions targeting keratosis pilaris, rough elbows and knees, and body acne.

Benefits or Advantages of Beta Hydroxy Acids (BHAs):
Beta Hydroxy Acids (BHAs) offer deep pore penetration due to their oil solubility, enabling exfoliation and sebum dissolution within the follicle where water-soluble acids such as AHAs cannot reach.
Beta Hydroxy Acids (BHAs) provide dual-action exfoliation working both on the skin surface by removing dead keratinocytes and within the pore by dissolving the sebum and dead cell mixture that causes blackheads and comedones.

Beta Hydroxy Acids (BHAs) have anti-inflammatory properties that set them apart from AHAs; salicylic acid in particular reduces redness, swelling, and irritation in acne lesions while simultaneously exfoliating, making Beta Hydroxy Acids (BHAs) gentler than AHAs for inflamed or acne-prone skin.
Beta Hydroxy Acids (BHAs) regulate sebum production over time, reducing excess oil and shine and preventing the pore-clogging conditions that lead to breakouts.

Beta Hydroxy Acids (BHAs) improve skin texture, tone, and clarity through consistent use, promoting cell turnover that reveals fresher, smoother skin and reduces the appearance of post-acne marks, hyperpigmentation, and uneven pigmentation.
Beta Hydroxy Acids (BHAs) are effective at lower concentrations than AHAs, requiring only 0.5 to 2% for effective daily exfoliation, compared to 5 to 10% or higher for AHAs to achieve comparable surface exfoliation.

Features of Beta Hydroxy Acids (BHAs):
Beta Hydroxy Acids (BHAs) are oil-soluble organic acids with a lipophilic character that distinguishes them from water-soluble AHAs and enables their unique ability to penetrate sebum-filled follicles.
Beta Hydroxy Acids (BHAs) are effective at a formulation pH of 3.0 to 4.0, with pH-dependent activation ensuring that the un-ionized form predominates and is membrane-permeable; products formulated above pH 4.5 will not deliver effective exfoliation regardless of BHA concentration.

Beta Hydroxy Acids (BHAs) encompass several compounds: salicylic acid is the dominant and most studied BHA; betaine salicylate is a newer, milder ester of salicylic acid derived from sugar beet; beta-hydroxybutanoic acid and trethocanic acid are less commonly used BHAs; and capryloyl salicylic acid (LHA) is a longer-chain derivative used for deeper, controlled peeling.
Beta Hydroxy Acids (BHAs) are keratolytic, meaning they dissolve the protein bonds (desmosomes) holding corneocytes together in the stratum corneum and within the follicular infundibulum, promoting desquamation and preventing comedone formation.

Chemical Properties of Beta Hydroxy Acids (BHAs):
Beta Hydroxy Acids (BHAs) are defined chemically as carboxylic acids with a hydroxyl substituent on the beta carbon; salicylic acid (2-hydroxybenzoic acid) is the archetypal BHA, with the hydroxyl group directly on the aromatic ring ortho to the carboxylic acid group, placing it structurally on the second carbon relative to the carbonyl.
Beta Hydroxy Acids (BHAs) owe their oil solubility to the presence of a lipophilic aromatic ring (in salicylic acid) or alkyl chain (in capryloyl salicylate), which provides hydrophobic character overriding the hydrophilicity of the carboxylic acid and hydroxyl groups.

Salicylic acid, the primary Beta Hydroxy Acid (BHA), has a molecular formula of C7H6O3, molecular weight of 138.12 g/mol, melting point of 158.6°C, density of 1.443 g/cm3, pKa of 2.97, and water solubility of 2.48 g/L at 25°C; it is freely soluble in ethanol, ether, acetone, and chloroform.
Beta Hydroxy Acids (BHAs) are chemically stable under normal storage conditions; salicylic acid is stable in dry form but may slowly degrade in aqueous solution, particularly at elevated temperatures or in the presence of oxidizing agents.

Production of Beta Hydroxy Acids (BHAs):
Beta Hydroxy Acids (BHAs) — particularly salicylic acid — are produced industrially through the Kolbe-Schmitt reaction, in which sodium phenolate is treated with carbon dioxide under pressure at elevated temperature (125°C) and subsequently acidified to yield salicylic acid.
Beta Hydroxy Acids (BHAs) derived from natural sources include salicylic acid obtained by hydrolysis of methyl salicylate from wintergreen oil or willow bark, though these natural extraction routes have largely been replaced by the more consistent and scalable Kolbe-Schmitt synthesis.

Beta Hydroxy Acids (BHAs) for pharmaceutical use are manufactured under GMP conditions and must meet pharmacopoeial specifications (USP, BP, EP) for assay, melting point, heavy metals, residue on ignition, and organic impurities.
Beta Hydroxy Acids (BHAs) for cosmetic use are subject to purity specifications in the EU Cosmetics Regulation and US FDA guidelines, including limits on impurities such as phenol and related compounds.

Material Safety Data Sheet (MSDS) of Beta Hydroxy Acids (BHAs):

Handling of Beta Hydroxy Acids (BHAs):
Beta Hydroxy Acids (BHAs) should be handled in accordance with good industrial hygiene and safety practices and in accordance with the relevant Safety Data Sheet for the specific compound.
Beta Hydroxy Acids (BHAs) handling requires avoiding inhalation of dust or aerosols, contact with eyes, and prolonged or repeated skin contact with concentrated solutions, which may cause irritation or chemical burns.

SDS of Beta Hydroxy Acids (BHAs):

Stability and Reactivity of Beta Hydroxy Acids (BHAs):

Chemical stability:
Beta Hydroxy Acids (BHAs) are stable under recommended storage and handling conditions when kept dry, cool, and away from oxidizing agents.

Reactivity:
No dangerous reaction is expected under normal conditions of use at cosmetic concentrations.
Beta Hydroxy Acids (BHAs) may react with strong oxidizing agents, strong bases, and reactive metals.

Conditions to avoid:
Excessive heat.
Direct sunlight and UV exposure.
High humidity and moisture (for solid forms).
Strong oxidizing agents.
Strong bases (alkalis).
Open flames and ignition sources.

Incompatible materials:
Strong oxidizing agents.
Strong alkalis.
Reactive metals (iron, aluminum, zinc) which may form salicylate salts.
Iodine and iodine-containing compounds.

Hazardous decomposition products:
Carbon monoxide (CO).
Carbon dioxide (CO2).
Phenol vapors (at thermal decomposition temperatures).
Irritating organic fumes.

Handling and Storage of Beta Hydroxy Acids (BHAs):

Handling:
Handle in accordance with good industrial hygiene and safety practices.
Avoid inhalation of dust or aerosol and prevent dust accumulation during weighing and mixing operations.
Avoid contact with eyes, mucous membranes, and prolonged skin contact with concentrated solutions.
Wash hands thoroughly after handling and before eating, drinking, or smoking.

Storage:
Store in tightly closed original containers in a cool, dry, and well-ventilated area.
Protect Beta Hydroxy Acids (BHAs) from heat, direct sunlight, moisture, and strong oxidizing agents.
Keep away from incompatible materials and reactive metals.
Recommended storage temperature: 15 to 25°C.
Shelf life: Typically 2 to 3 years in original sealed packaging under recommended conditions.

First Aid Measures of Beta Hydroxy Acids (BHAs):

Inhalation:
Remove affected person to fresh air.
If dust or aerosol causes respiratory irritation or discomfort, seek medical attention.

Skin contact:
Wash affected skin immediately with soap and plenty of water.
Remove contaminated clothing.
Concentrated solutions of Beta Hydroxy Acids (BHAs) may cause skin irritation, chemical burns, or sensitization; seek medical advice promptly if symptoms occur.

Eye contact:
Immediately flush eyes with clean running water for at least 15 minutes while holding eyelids open.
Remove contact lenses if present and easy to do.
Seek immediate medical attention; Beta Hydroxy Acids (BHAs) in concentrated form are corrosive to eyes.

Ingestion:
Rinse mouth thoroughly with water.
Do not induce vomiting unless directed by medical personnel.
Seek immediate medical attention; ingestion of salicylic acid can cause salicylate toxicity with symptoms including nausea, tinnitus, and metabolic disturbances.

Firefighting Measures of Beta Hydroxy Acids (BHAs):

Suitable extinguishing media:
Water spray, foam, dry chemical powder, or carbon dioxide.

Specific hazards:
Beta Hydroxy Acids (BHAs) in solid form may burn under fire conditions and generate irritating fumes.
Thermal decomposition of Beta Hydroxy Acids (BHAs) may produce carbon monoxide, carbon dioxide, phenol vapors, and irritating organic fumes.

Protective equipment for firefighters:
Wear self-contained breathing apparatus (SCBA) and full protective clothing.

Firefighting instructions:
Avoid generating dust during firefighting operations.
Prevent contaminated firefighting water from entering drains or waterways.

Accidental Release Measures of Beta Hydroxy Acids (BHAs):

Personal precautions:
Avoid breathing dust or aerosol.
Use appropriate personal protective equipment during cleanup.
Ensure adequate ventilation in the affected area.

Environmental precautions:
Prevent large quantities of Beta Hydroxy Acids (BHAs) from entering drains, sewers, or natural waterways.

Methods for cleaning up:
Collect spilled solid material carefully by sweeping or vacuuming to minimize dust generation.
For liquid spills, contain with inert absorbent material such as sand or vermiculite.
Transfer into suitable labeled containers for reuse or disposal according to local regulations.
Wash contaminated surfaces with water after bulk material has been removed.

Exposure Controls / Personal Protective Equipment of Beta Hydroxy Acids (BHAs):

Engineering controls:
Provide adequate general or local exhaust ventilation where dust or aerosol may be generated.

Respiratory protection:
Not normally required under standard cosmetic or pharmaceutical handling conditions.
Use an approved particulate respirator when handling large quantities of dry powder.

Hand protection:
Wear chemical-resistant gloves during handling of concentrated solutions.

Eye protection:
Wear safety glasses or chemical splash goggles where dust or splashing is possible.

Skin and body protection:
Wear suitable protective clothing when handling concentrated solutions of Beta Hydroxy Acids (BHAs).

Hygiene measures:
Do not eat, drink, or smoke while handling Beta Hydroxy Acids (BHAs).
Wash hands thoroughly after handling.

Identifiers of Beta Hydroxy Acids (BHAs):
Class: Beta Hydroxy Acids (BHAs)
Primary compound: Salicylic Acid
CAS No. (Salicylic Acid): 69-72-7
EC No. (Salicylic Acid): 200-712-3
PubChem CID (Salicylic Acid): 338
ChemSpider (Salicylic Acid): 331
ChEBI: CHEBI:16914
ChEMBL: ChEMBL424
DrugBank: DB00936
KEGG: D00097
UNII: O414PZ4LPZ
ECHA InfoCard: 100.000.648
RTECS: VO0525000
InChIKey (Salicylic Acid): YGSDEFSMJLZEOE-UHFFFAOYSA-N
SMILES (Salicylic Acid): OC(=O)c1ccccc1O
IUPAC Name (Salicylic Acid): 2-hydroxybenzoic acid
FDA Classification: OTC active ingredient for acne (0.5–2%)
EU Cosmetics Regulation: Listed in Annex III with restrictions (max 2% in face products; max 3% in rinse-off hair products)

Properties of Beta Hydroxy Acids (BHAs) — Salicylic Acid:
Physical state: Solid (crystalline powder)
Appearance: Colorless to white crystalline powder
Odor: Odorless
Density: 1.443 g/cm3 (20°C)
Melting point: 158.6°C
Boiling point: 211°C (at 20 mmHg); sublimes at 76°C
pKa: 2.97
Solubility in water: 1.24 g/L (0°C); 2.48 g/L (25°C); 77.79 g/L (100°C)
Solubility in organic solvents: Soluble in ethanol, ether, acetone, chloroform, toluene; freely soluble in propanol
Oil solubility: Yes (lipophilic; soluble in oils and sebum)
Effective pH range: 3.0–4.5 (un-ionized, membrane-permeable form)
Optimal formulation pH: 3.0–4.0

Specifications of Beta Hydroxy Acids (BHAs) — Salicylic Acid:
Chemical name: Salicylic Acid (2-Hydroxybenzoic Acid)
Molecular formula: C7H6O3
Molecular weight: 138.12 g/mol
CAS Number: 69-72-7
Assay (dried basis, USP/EP): ≥99.5%
Melting point: 158–161°C
Loss on drying: ≤0.5%
Residue on ignition: ≤0.05%
Heavy metals (as Pb): ≤20 ppm
Phenol and related impurities: ≤0.05%
Typical cosmetic use concentration: 0.5–2.0% (leave-on); up to 3% (rinse-off hair products, EU)
Professional peel concentration: 10–30%
FDA OTC acne product: 0.5–2%
Storage conditions: Store in tightly closed containers at 15 to 25°C, dry, away from heat and direct sunlight

Names of Beta Hydroxy Acids (BHAs):
Beta Hydroxy Acid
Beta-Hydroxy Acid
BHA
BHAs
Salicylic Acid (primary BHA)
2-Hydroxybenzoic Acid
Orthohydroxybenzoic Acid
Betaine Salicylate
Beta-Hydroxybutanoic Acid
Trethocanic Acid
Capryloyl Salicylic Acid (LHA)
Willow Bark Extract (natural source)
Oil-Soluble Exfoliant
Lipophilic Hydroxy Acid
Chemical Exfoliant BHA