Ingredient intelligence
Caffeine
Hair biology · Caffeine · C8H10N4O2
Caffeine is a methylxanthine and phosphodiesterase inhibitor studied in hair-follicle organ culture and in microcirculation-related cosmetic research.
Molecular identity
- Formula
- C8H10N4O2
- Molecular weight
- 194.19 g/mol
- PubChem CID
- 2519
- ChEBI
- CHEBI:27732
Biological targets
cAMP-specific phosphodiesterase 4 (PDE4B)
medium confidenceinhibits · enzyme
UniProt Q07343Adenosine receptor A2a (ADORA2A)
high confidenceinhibits · receptor
UniProt P29274
How could this ingredient interact with biology?
Biological network
Ingredient → molecule → target → gene/protein → pathway → process → studied outcome. Relationship strength is drawn from the curated confidence tier; nothing is added to make the chain look complete.
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3 lower-confidence relationships are hidden at this filter level. Use “Show more biology” to include them.
Text alternative for this network
- Caffeine is molecule Caffeine — high confidence
- Caffeine inhibits cAMP-specific phosphodiesterase 4 (PDE4B) — medium confidence
- Caffeine inhibits Adenosine receptor A2a (ADORA2A) — high confidence
- Adenosine receptor A2a (ADORA2A) encoded by ADORA2A — high confidence
- cAMP-specific phosphodiesterase 4 (PDE4B) encoded by PDE4B — medium confidence
- ADORA2A participates in Adenosine receptor signalling — high confidence
- PDE4B participates in Adenosine receptor signalling — medium confidence
- ADORA2A participates in cAMP signalling — medium confidence
- PDE4B participates in cAMP signalling — medium confidence
Biological pathways
Adenosine receptor signalling
high confidenceCompetitive adenosine receptor antagonism.
Reactome R-HSA-417973
cAMP signalling
medium confidencePhosphodiesterase inhibition raises intracellular cAMP.
Reactome R-HSA-418555
Evidence engine
Insufficient
Not enough curated evidence to characterise this ingredient.
Skinceptor Evidence Index
12
experimental · of 100
This index is a research-navigation aid describing how much evidence exists and how it was produced. It is not a medical safety score, an efficacy guarantee, or a clinical recommendation.
Study composition
- In-vitro1
- Total studies
- 1
- Human studies
- 0
- Largest sample
- Data unavailable
- Range
- 2007–2007
Index breakdown
- Study design quality25% × 28%
Mean design weight across curated studies (meta-analysis 1.0, RCT 0.9, other human 0.7, review 0.45, animal 0.35, in-vitro 0.25).
- Human evidence share0% × 22%
Proportion of curated evidence measured in people rather than cells or animals.
- Evidence volume32% × 14%
Log-scaled count of curated studies, so volume alone cannot dominate the score.
- Largest sample size0% × 12%
Log-scaled largest reported sample size across curated human studies.
- Replication0% × 12%
Independent human studies, capped at three; one study is never treated as replicated.
- Recency5% × 7%
Linear decay over a twenty-year window from the most recent curated publication.
- Source traceability0% × 5%
Share of curated studies with a verified PMID or DOI in this dataset.
Insufficient comparable evidence for quantitative synthesis.
Research timeline
How the evidence accumulated
2007
Caffeine and human hair follicle growth in organ culture
In-vitrosample size unavailable · International Journal of Dermatology
Ingredient fingerprint
11 nodes · 15 relationships · seed "caffeine"
The fingerprint is a deterministic visual signature: ridge amplitude comes from the number of entities in each tier, node placement from identifier hashes, and opacity from confidence. Two ingredients can never produce the same figure unless their networks are identical.
Open in Biology as Art →Research
1 curated study
Caffeine and human hair follicle growth in organ culture
Reported counteraction of testosterone-suppressed hair shaft elongation in ex-vivo follicle culture.
Limitations — Organ culture; topical delivery to the follicle in vivo not established; identifier not verified.
Community evidence
Submitted by readers
Reader submissions appear here only after review. They are not part of the curated dataset and do not affect the Skinceptor Evidence Index.
No approved community submissions yet.
Sources
- PubChem 2519retrieved 2026-09-14
- Reactome R-HSA-417973retrieved 2026-09-14
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