PABA

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paba

What is PABA

PABA (C7H7NO2) also called para-aminobenzoic acid or 4-aminobenzoic acid, is a natural substance that naturally occur in these foods: brewer’s yeast, liver, kidney, molasses, mushrooms, spinach, whole grains and eggs 1, 2, 3, 4, 5. PABA is sometimes called vitamin Bx or vitamine B10, but it is not a true vitamin. PABA (para-aminobenzoic acid or 4-aminobenzoic acid) is a potent ultraviolet B (UVB) absorber but do not absorb ultraviolet A (UVA). PABA (para-aminobenzoic acid) is often used in sunscreen and skin-care products. When used appropriately, PABA-containing products can reduce the incidence of several types of skin cancers by reducing the amount of harmful ultraviolet B (UVB) radiation which can act upon the skin 6, 7, 8. The U.S. Food and Drug Administratio (FDA) regulates sunscreen as an over-the-counter medication. Because some people are allergic to PABA (allergic and photoallergic skin reactions), the U.S. Food and Drug Administration (FDA) in 2021 issued non-GRASE (not generally recognized as safe and effective) status for sunscreens containing PABA 9, 10. Furthermore, the 2021 FDA Sunscreen for Over-the-Counter Human Use Monograph M020 identified zinc oxide and titanium dioxide (in any form) as GRASE (generally recognized as safe and effective) 9, 10. The US FDA regulates PABA use at a maximum of 15% concentration, while octyl-dimethyl-p-aminobenzoate (OD-PABA or Padimate O) is regulated at a maximum of 8% concentration 9. Swallowing sunscreen products containing PABA rarely causes symptoms, except in very large doses. PABA allergy is diagnosed by performing special allergy tests, i.e. patch tests with 10% PABA in petrolatum 5, 11.

Symptoms of an allergic reaction to PABA or PABA overdose include:

  • Diarrhea
  • Dizziness
  • Eye irritation if it touches the eyes
  • Fever
  • Liver failure
  • Nausea, vomiting
  • Rash (in allergic reactions)
  • Shortness of breath
  • Slowed breathing
  • Stupor (altered thinking and decreased level of consciousness)
  • Coma (unresponsiveness)

If you are diagnosed with PABA allergy then avoid exposure to PABA-containing products. Management of PABA dermatitis may be treated as for any acute dermatitis or eczema; this may include treatment with topical corticosteroids and moisturizers.

PABA derivative called octyl-dimethyl-p-aminobenzoate (OD-PABA or Padimate O) is used in place of PABA as an effective ultraviolet B (UVB) absorber in sunscreens and is less likely to cause hypersensitivity reactions or stain clothing 12, 13, 14. Padimate O (OD-PABA) may also disrupt endocrine activity 15.

Currently, cinnamates have replaced PABA as the next most potent ultraviolet B (UVB) absorber and include octinoxate (OMC) and cinoxate 13. Octinoxate is the most commonly used UVB filter in the United States 16. It is not as potent a UVB absorber as octyl-dimethyl-p-aminobenzoate (OD-PABA or Padimate O); for this reason, other UVB absorbers are used in combination to increase the sun protection factor (SPF). An SPF-15 can block 94% of UVB radiation, while an SPF-30 can block 97% of UVB radiation 12. SPF-15 or higher is the recommended sunscreen blocking strength, and manufacturers can label it as reducing the risk of skin cancer and early skin aging 17. Octinaxate is not very photostable and degrades in the presence of sunlight after a short period. Cinnoxate is a less common choice 12.

Salicylates are used in high concentrations as they are weak ultraviolet B (UVB) absorbers 16. Salicylates are also used to increase the effect of other UVB filters. Two salicylates that are FDA listed are homosalate and octisalate. They function to decrease the photodegradation of other UV filters, such as oxybenzone and avobenzone. A water-soluble salicylate is trolamine salicylate 12.

Octocrylene is a very safe chemical associated with a decreased likelihood of irritation, phototoxicity, and photoallergic potential 18. When combined with other UV absorbers, it can increase the sun protection factor (SPF) rating 13.

Ensulizole is a pure UVB filter and does nothing that affects ultraviolet A (UVA). It is a water-soluble compound commonly used in cosmetics for a lighter, less oily feel 13.

Camphor derivatives are not FDA-listed but are moderately effective UVB filters. A camphor derivative that is also a broad ultraviolet A (UVA) filter is terephthalyidene dicamphor sulfonic acid 12.

Figure 1. PABA food sources

PABA food sources
[Source 19 ]

Figure 2. PABA in sunscreens

PABA in sunscreens
[Source 19 ]

What should I do to avoid PABA allergy?

Read product labels and avoid products that contain PABA or any of its alternative names.

PABA other names 5:

  • Para-Aminobenzoic acid
  • P-Aminobenzoic acid
  • Aminobenzoic acid
  • 4-Aminobenzoic acid
  • Para-Aminobenzoate
  • Aminobenzoate Potassium
  • ABA
  • Ethyl Dihydroxypropyl Aminobenzoate
  • Glyceryl Paraaminobenzoate
  • Octyl Diemthyl PABA
  • Padimate O
  • Bacterial Vitamin H1
  • Vitamin B10
  • Vitamin Bx
  • Vitamin H1
  • Vitamine B10

Avoid related substances that you may also be allergic to. This includes sunscreen products containing PABA esters (e.g., glyceryl PABA, padimate O, benzocaine, procaine), paraphenylenediamine (PPD) commonly found in permanent hair dyes, sulfonamides, and azo dyes. Ask your pharmacist for advice and a suitable alternative. Alert your doctor and dentist to the fact that you have an allergy to PABA. Your skin doctor (dermatologist) may have further specific advice, particularly if you are highly sensitive.

PABA benefits

PABA (para-aminobenzoic acid or 4-aminobenzoic acid) is found in various foods such as grains, milk, eggs, and meat and has extensive usage in the chemical industry as a starting material for the preparation of folate (vitamin B9), a crucial vitamin required for DNA synthesis and replication 20, 21. In folic acid synthesis, PABA is a necessary and irreplaceable vitamin of group B 22, 23. Through folic acid breakdown, it is also produced in the human body 24. Although PABA is not synthesized in mammals and humans, it is a constant component of metabolism due to the supply of food and symbiotic bacteria (Escherichia coli), which continuously produce PABA in mammals 25. PABA is also a biologically active compound that is frequently found as a building block for drugs with usages ranging from antimicrobial to UV protectants 19. Overall, the chemistry of PABA is diverse and plays a crucial role in various biological and industrial processes 26, 27.

PABA (para-aminobenzoic acid or 4-aminobenzoic acid) is also used for the production of hair dyes and sunscreens due to its ability to absorb UV radiation 28. Para-aminobenzoic acid (PABA) is closely related chemically to salicylate 29. Salicylates are a group of natural chemicals found in plants and many medications. Salicylates are weak ultraviolet B (UVB) absorbers and they are generally used in combination with other UV filters 13. PABA is a potent ultraviolet B (UVB) absorber but does not absorb ultraviolet A (UVA). In 1943 PABA was patented and became one of the first active ingredients to be used in sunscreen products. Although PABA and its aminobenzoic acid esters (glyceryl PABA, padimate O and roxadimate) are all effective sunscreen agents, they are also strong sensitizing agents and can cause allergic contact dermatitis. PABA was reportedly the most common photoallergen and contact allergen. Also, in the early 1980s, animal studies with PABA suggested there may be an increased risk of cellular UV damage. In 2021 the FDA issued non-GRASE (not generally recognized as safe and effective) status for sunscreens containing PABA 9, 10. For these reasons PABA is now seldom used in sunscreen products.

PABA is also used as an ingredient in hair care formulations for premature greying and hair loss, but more studies are needed to support these uses.

PABA is also the chemical foundation for a group of local anesthetic agents. These include butethamide, benzocaine, procaine, tetracaine, propoxycaine, and butacaine. Allergic contact dermatitis reactions may occur when these agents are used in PABA sensitive individuals. Benzocaine is the most notorious sensitizer.

Table 1. Therapeutic potential of PABA derivatives

PABA derivativesSynthetic ConditionsCharacterization
Techniques		Physical PropertiesBiological ActivityIC50 (µM)Reference
Nonyl (4-nonylamino) benzoatePABA, alkylating agent, K2CO3, acetone, 5–6 hEIMS, FTIR, 1H-NMR, and 13C NMRAmorphous white solidCytotoxicity activity against the NCI-H460 cell lineNCI-H460: 15.5930
4-31
N-(tert-butyl)-4-(2-(3-methyl-2-oxoquinoxalin-1(2H)-yl)acetamido) benzamideN-(tert-butyl)-4-(2-chloroacetamido) benzamide, potassium salt of 3-methylquinoxalin-2(1H)-one, DMF, KI, heating 3 h1H NMR, 13C NMR, and FTIRDark green crystal,
Yield: 80%,
m.p: 230–232 °C		Cytotoxicity against HepG2 and MCF-7 cell linesMCF-7: 7.7, HepG2: 4.532
2-(4-33
34
3α-O-(4-acrylamidebenzoyl)-4β-hydroxy-5,7α,6β(H)-guaia-1(10),11(13)-dien-12,6-olide3α,4β-dihydroxy-5,7α,6β(H)-guaia-1(10),11(13)-dien12,6-olide, 4-acrylamidobenzoic acid, DCC, DMAP, CH2Cl2,1H NMR, 13C NMR, and HRESIMSWhite powder,
Yield: 56%,
m.p: 120–122 °C		Cytotoxicity against Huh7 and HepG2 cell linesHepG2: 7.9 ± 0.3
Huh: 78.5 ± 0.2		35
Ag-PABA complexPABA, KOH, AgNO3, 1 hXRD, mass spectrometry, 1H NMR, 2D NMR, and 13C NMRWhite solidIn vitro antibacterial activityMIC value (µM)
S. aureus ATCC 25923: 88.5
B. cereus ATCC 14579: 88.5
E. coli: 44.0		36
4-[1-(1,3-Dihydro-benzoimida-zol-2-ylideneamino)-oct-2-ynylideneamino]-benzoic acidOct-2-ynoic acid (1,3-dihydrobenzoimidazole-2-ylidene)amide, aniline derivatives, warm ethanoic solution and refluxing for 4 hUV–Vis absorption, FTIR, 13C NMR, 1H NMR, and C, H, N elemental analysisWhite powder,
Yield: 73%,
m.p. 175.2 °C		Anti-plasmodial activityPlasmodium Falciparum 3D7:
28.31 µg/mL		37
Peanut skin extract-azo-compounds and complexes with ironNaNO2, HCl, ice, peanut skin extract,
FeCl2, methanol, 65 °C, reflux 3 h		SEM-EDS analysis, FTIR, and UV-visible spectroscopyDeep orange, Yield: 56.81%,
m.p: > 300 °C		Antimicrobial activity against Staphylococcus aureus and Escherichia coliInhibition zone (mm)
E. Coli:10.0 ± 0.33
S. aureus: 6.0 ± 1.52		38
4-(1H-Indole-2-carboxamido) benzoic acidDry pyridine, CHCl3,1H-Indole-2-carbonyl chlorideNMR, IR spectroscopy, HRMS, and elemental analysis techniquesYield: 86%,
m.p: 256–258 °C		Antifungal and antibacterial activityInhibition zone (mm)
C. albicans DSMZ 11949: 9–14		39
Methyl (S)-2-(4-(4-methylphenylsulfonamido) benzamido)propanoateAmino acid methyl ester hydrochloride, 4-(4-methylphenylsulfonamido)benzoic acid, DCC, HOBt, DIPEA, THF,1H NMR, 13C NMR, and HRMSYield: 92%,
m.p. 203.1–203.9 °C		In vitro PPRE-activated activityPPRE-activated activity: 87%40
2-41
N,N’-(1,2-phenylene) bis(4-aminobenzamide) and its complexesethyl 4-aminobenzoate, 1,2-Benzene diamine, reflux 3 h,
MCl2, reflux		UV-Vis, FTIR, 1H NMR, and elemental analysesPale green,
Yield: 45%,
m.p: 230 °C		Antibacterial activity against S. aureus and E. coliDiameters of antibacterial activity
S. aureus: 25 mm
E. coli: 28 mm		42
N-(2-(1-benzylpiperidin-4-yl)ethyl)-4-43
N-(4-{[(2E)-2-(4-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranoside)-3-metoxybenzylidene)hydrazino]carbonyl}phenyl)benzamidegalactoside, N-(4-(hydrazinecarbonyl)phenyl)benzamide, ethyl alcohol, r.t, HCl, stirring for 24 h13C NMR, 1H NMR
HRMS (ESI), and FTIR		White crystals,
Yield: 84%, m.p: 137–138 °C		Antifungal activityC. glabrata: 695.244
4-(4-(1-(2-Isonicotinoylhydrazono)ethyl)phenylsulfonamido)benzoic acidAcetylbenzenesulfonamide derivatives, hydrazide derivatives, methanol, 2 h, glacial acetic acidUV, IR, 1H NMR, 13C NMR, mass spectroscopy, and elemental analysisWhite solid, Yield: 41%
m.p: 288–290 °C		AChE activityAChE: 11.12 ± 0.7445
N-(3-(Hydroxycarbamoyl)phenyl)-3,5,6-Trimethylpyrazine-2-Carboxamide4-(3,5,6-trimethylpyrazine-2-carboxamido)benzoic acid, NH2OH,1H NMRYield: 52%
m.p: >250 °C		Antiproliferative activities against two HDAC-expressing cancer cell lines: HT-29 and SH-SY5YHT-29 cells: 1.9646
Cu(PABA)2(H2O)2 complexMetal and ligand 1:2 molar ratio (M:L), 30 min, pH value at 5.6, r.tFTIR and UV-vis spectroscopyDark green productAntimicrobial activityInhibition zone (mm)
Enterococcus faecalis: 16 S. aureus: 11		47
4-(2-(4-(1H-Benzimidazol-2-yl)phenyl)hydrazono)-1-(4-chlorophenyl)-3-methyl-1H-pyrazol-5(4H)-oneEthyl 2-(2-(4-(1H-benzimidazol-2-yl)phenyl) hydrazono)-3-oxobutanoate, hydrazine hydrochloride, ethanol, refluxed for 12 hEIMS, FTIR, 1H NMR, and 13C NMRYield: 82%, m.p: 197–200 °CAntimicrobial activityMIC (µg/mL)
S. aureus: 7.81
S. epidermidis: 1.95
E. coli: 7.81		48
[Source 19 ]

Is PABA safe?

In vivo and in vitro animal studies have shown PABA to be an endocrine disruptor or chemical that can interfere with your body’s hormones affecting the reproductive and developmental systems.

Para-aminobenzoic acid (PABA) inhibits iodide binding in the thyroid gland and disrupts the thyroid’s production of hormones 49, 50. Para-aminobenzoic acid (PABA) also displaces thyroid hormone from its serum protein-binding (thyroxine-binding globulin) sites 51. Abnormalities of thyroid function tests have been also reported in patients treated with salsalate (a medication that belongs to the salicylate and nonsteroidal anti-inflammatory drug classes) 52.

Studies performed on rats and on thyroid tissue samples suggest that PABA may disrupt thyroid activity 53, 54, 55. In a study conducted on thyroid tissue samples, researchers found that PABA inhibited thyroxine (T4), the primary hormone secreted by the thyroid gland that regulates metabolism 54. Decreased levels of thyroxine (T4) may lead to underactive thyroid (hypothyroidism) which includes symptoms such as fatigue, weight gain, and muscle weakness 56.

The PABA derivative Padimate O (OD-PABA) appears to be weakly anti-estrogenic meaning it suppresses estrogen pathways 15. Estrogen is a hormone that helps develop and regulate the female reproductive system. It also affects other parts of the body, including the heart, bones, brain, and skin. The mechanism of action behind the reproductive toxicity may be due to alterations in proteins of the gene expression of estrogen receptor, androgen receptor, progesterone receptor, insulin-like growth factor I, complement proteins, nuclear receptor co-repressor, and steroid receptor coactivator 1 in the uterus and prostate. In a 90-day study with a derivative of PABA called benzophenone-3 (BP-3), fertility was affected in male mice. This finding was demonstrated by decreased sperm density in a dose-related manner following dermal exposure in mice and oral exposure in mice and rats 57.

Experimental studies in humans have demonstrated an increased permeability of the UV filters benzophenone-3 (BP-3), 4-methylbenzylidene camphor (4-MBC also known as enzacamene), and octinoxate (OMC) 16. Levels were detectable in the plasma 1 to 2 hours after exposure. The study also demonstrated a difference in concentration based on gender. Male urine and plasma concentration samples were higher than female samples 16. A Swiss study of human breast milk revealed that 85% of the sample contained UV filters. Bisphenol and benzophenone-3 (BP-3) share a similar chemical structure. Bisphenol can cross the blood-placenta barrier, so the assumption is that benzophenone-3 (BP-3) can also cross the placenta. An increased concentration of benzophenone-3 (BP-3) in a mother’s urine was associated with decreased birth weight in girls and increased birth weight and head circumference in boys 57.

Another PABA derivative, ethyl-4-aminobenzoate (Et-PABA), disrupts estrogenic and androgenic activity in fish 58.

PABA side effects

PABA sensitivity produces classic allergic contact dermatitis as well as photocontact dermatitis (an inflammatory skin reaction that occurs when ultraviolet or visible light interacts with a topically applied or systemically taken photoreactive substance on or in the skin). In PABA allergic individuals, sunscreens containing PABA or its esters can cause a burning or stinging sensation particularly if the product is alcohol-based. However, burning and stinging may also sometimes occur as an irritant reaction in people with sensitive skin, even when not actually allergic to PABA.

In Germany, a 15-year study of patch and photo patch testing demonstrated that the most common reaction to sunscreen is a nonimmune-based irritant response 59. The most common UV filters that cause adverse effects are benzophenones and dibenzoylmethanes, with the most common photoallergen being benzophenone-3 (BP-3), as it is a derivative of PABA. For this reason, benzophenone 3 is not used frequently in the United States 59. Some studies have associated sunscreen use with melanoma due to the users’ false sense of security, which may increase the duration in the sun, resulting in UVA formation and cancer changes 60. Phototoxic and allergic contact dermatitis are usually the results of UVA (320 to 400 nm) and visible light ranges (400 to 800 nm). UVA is capable of penetrating the reticular dermis and is the cause of most photosensitivity reactions 61.

Occasionally injection of PABA-derived local anaesthetics to allergic individuals may cause swelling of the oral mucosa (stomatitis) at the site of the injection. Rarely, more severe reactions such as generalized urticaria also called hives (red and sometimes itchy bumps on your skin due to allergic reaction) or anaphylaxis (a serious life-threatening allergic reaction) may result.

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  31. 5,6,7,8-tetrahydrobenzo [4,5]thieno [2,3-d]pyrimidin-4-yl)amino) benzoic acid4-chloro-6,7,8,9-tetrahydro-5H-indeno [2,1-d]pyrimidine, PABA, ethanol, reflux, 4 hEIMS, FTIR, 1H NMR, and 13C NMRYellow crystal,
    Yield: 88%,
    m.p: 280–282 °CCell lines: EGFRT790M and HER2 kinases and 4 cancer cell lines of HCT-116, HepG2, A431, and MCF-7HepG2: 67.72 ± 3.70
    HCT-116:
    62.57 ± 3.30
    MCF-7:
    75.75 ± 3.40((Elmetwally S.A., Saied K.F., Eissa I.H., Elkaeed E.B. Design, synthesis and anticancer evaluation of thieno [2, 3-d] pyrimidine derivatives as dual EGFR/HER2 inhibitors and apoptosis inducers. Bioorgan. Chem. 2019;88:102944. doi: 10.1016/j.bioorg.2019.102944[↩]
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  33. 2-Oxoindolin-3-ylidene)amino)benzoyl)-N-phenylhydrazinecarbothioamide4-((5-Substituted-2-oxoindolin-3-ylidene)amino)benzohydrazide,
    Isothiocyanatobenzene, EtOH, Reflux, 8 h.EIMS, FTIR, 1H NMR, and 13C NMRYellow powder,
    Yield: 93%,
    m.p: 211–213 °CCytotoxic activity
    against HepG2 cell line, MCF-7 cell line,
    VEGFR-2 kinase inhibitory assayMCF-7: 0.74–4.62 HepG2: 1.13–8.81 VEGFR-2: 0.078((Abdelgawad M.A., Hayallah A.M., Bukhari S.N.A., Musa A., Elmowafy M., Abdel-Rahman H.M., Abd El-Gaber M.K. Design, Synthesis, Molecular Modeling, and Anticancer Evaluation of New VEGFR-2 Inhibitors Based on the Indolin-2-One Scaffold. Pharmaceuticals. 2022;15:1416. doi: 10.3390/ph15111416[↩]
  34. E)-N-(3-(1-(2-(4-(2,2,2-Trifluoroacetamido)benzoyl)hydrazono)ethyl)phenyl)nicotinamide)2,2,2-Trifluoro-N-(4-(hydrazinecarbonyl)phenyl)acetamide, N-(3-acetylphenyl)nicotinamide, 6 h and absolute ethanolEIMS, FTIR, 1H NMR, and 13C NMROff-white crystals
    Yield: 80%,
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