Table 1 Key Amino Acid Biomarkers in Sweat, Their Properties, and Associated Health Conditions

Tyrosine

Polar, Amphipathic

Phenol group

Conditionally Essential

Tyrosinemia, Non-Alcoholic Liver Disease, Neuropsychiatric disorders, Alkaptonuria, Depression

112 ± 23

^{43,44,45,46,47}

Leucine

Non-polar, Hydrophobic

Isobutyl group (Branched chain)

Essential

Type 2 Diabetes, Diabetic Retinopathy, Sarcopenic Risk

112 ± 7.2

^48,49,50

Glycine

Non-polar (often considered neutral)

Hydrogen atom

Conditionally, Non-Essential

Cardiovascular Disease, Type 2 Diabetes, Cognitive Decline

1024 ± 122

^51,52,53,54

Phenylalanine

Non-polar, Hydrophobic

Benzyl group (Aromatic)

Essential

Phenylketonuria (PKU), Parkinson’s Disease, Heart Failure, Alkaptonuria, Radiographic Knee Osteoarthritis

203 ± 14.4

^45,55,56,57

Arginine

Positively Charged, Polar, Basic

Guanidinium group

Conditionally Essential

Cardiovascular Disease (Hypertension, atherosclerosis, HF, CAD), Depression

13.8 ± 9.5

^{58,59,60,61,62}

Citrulline

Polar, Neutral

Ureido group

Non-Essential

Cardiovascular Disease, Type 2 Diabetes, Depression

8.2 ± 5.2

^61,62,63,64

Serine

Polar, Uncharged

Hydroxymethyl group

Conditionally, Non-Essential

Alzheimer’s Disease, Kidney Disease, Cancer

1664 ± 128

^{53,54,65,66,67}

Alanine

Non-polar, Hydrophobic

Methyl group

Non-Essential

Type 2 Diabetes, Sarcopenia, Gestational Diabetes Mellitus

458 ± 8.0

^51,68,69

Ornithine

Positively Charged, Polar, Basic

3-aminopropyl group

Non-proteinogenic, Conditionally, Essential

Depression, Parkinson’s, Bladder Cancer, Cardiovascular Disease (Through GABR)

302.76 ± 139.41

^{55,61,70,71,72}

Tryptophan

Non-polar, Hydrophobic

Indole group (Aromatic)

Essential

Cancer, Neurodegenerative Disease

43.27 ± 20.25

^{38,39,40,73,74,138}