mechanism
The causal process or action by which something occurs—answering HOW rather than WHAT. Describes the biological, chemical, or physical means by which a cause produces an effect.
Why This Property Exists
Schema.org's medical vocabulary can describe what happens—a condition, a symptom, a treatment outcome—but lacks vocabulary for expressing how biological processes unfold mechanistically.
Consider the difference:
- What happens: "Rapid weight loss causes hair shedding"
- How it happens: "Metabolic stress signals follicles to synchronously enter telogen phase"
The second version captures the actual biological process—the mechanism—that connects cause to effect. This mechanistic detail is essential for:
- Medical education: Understanding pathophysiology requires knowing the steps, not just the endpoints
- Treatment rationale: Interventions target specific mechanisms, not just outcomes
- LLM reasoning: Language models can provide better explanations when they have access to causal chains rather than just associations
- Knowledge graphs: Mechanistic relationships enable richer queries than simple cause-effect links
The mechanism property fills this gap by capturing the means by which causes produce effects, making implicit biological knowledge explicit and machine-readable.
Domain and Range
Used On (Domain)
| Type | Context |
|---|---|
| hs:CausalStep | Primary use. Each step in a causal pathway describes its mechanism. |
| hs:ContributingFactor | Explains how a risk factor contributes to a multifactorial condition. |
Expected Values (Range)
| Type | Notes |
|---|---|
| schema:Text | Free text description of the causal process. Should describe an action or process, not a state. |
Distinction From Related Properties
Several properties describe aspects of causation. Here's how they differ:
| Property | Captures | Answers | Example |
|---|---|---|---|
| mechanism | The process/action | "By what means?" | "TGF-β binds to receptor complex, phosphorylating SMAD proteins" |
| result | The immediate outcome | "What happened?" | "Increased collagen gene transcription" |
| description | General explanation | "What is this?" | "A growth factor signaling pathway involved in tissue repair" |
| initialCause | Starting point | "What triggered this?" | The BiologicalProcess or event that begins the pathway |
| finalOutcome | End state | "What's the ultimate effect?" | The MedicalCondition or state produced by the entire pathway |
The Key Test
If your text describes a verb (binding, signaling, phosphorylating, inhibiting)—it's a mechanism.
If your text describes a noun or state (increased levels, cell death, inflammation)—it's a result.
Usage Guidance
Do
- Write mechanisms as active processes—use verbs that describe actions
- Be specific about biological actors—name the proteins, cells, or structures involved
- Include appropriate biochemical detail—match the level of detail to your audience
- Reference other entities via @id—link to proteins, anatomical structures, or other defined entities in your schema
Don't
- Describe states or outcomes—those belong in
result - Be vague—"causes inflammation" is less useful than "activates NF-κB pathway, triggering cytokine release"
- Conflate multiple steps—if there are distinct sequential events, use separate CausalSteps
Level of Detail
Match the granularity to your content's purpose:
- Patient-facing content: "Growth factors signal skin cells to produce more collagen"
- Professional content: "TGF-β binds TGF-β receptor complex, activating SMAD2/3 phosphorylation"
- Research-level: "TGF-β1 ligand binding induces TβRII/TβRI heteromeric complex formation, triggering TβRI kinase domain activation and subsequent SMAD2 C-terminal serine phosphorylation"
Examples
Example 1: CausalStep in a Pathway
From a PRP therapy mechanism:
{
"@type": "CausalStep",
"stepNumber": 2,
"mechanism": "Growth factors bind to receptor tyrosine kinases on target cell surfaces",
"result": "Receptor dimerisation and autophosphorylation, activating intracellular signaling cascades"
}Why this works: The mechanism describes the action (binding), the actors (growth factors, receptor tyrosine kinases), and implies the biochemical process. The result describes what happens as a consequence.
Example 2: ContributingFactor Mechanism
From a multifactorial hair loss condition:
{
"@type": "ContributingFactor",
"factorName": "Inadequate protein intake",
"importance": "Major",
"mechanism": "Hair is 90% protein (keratin); insufficient dietary protein means follicles lack building blocks for hair shaft synthesis",
"modifiable": true,
"interventions": [
"Calculate individual requirements: 1.2-2.0 g/kg daily",
"Track intake for at least 3 days"
]
}Why this works: The mechanism explains why low protein causes hair problems—it connects the dietary factor to the biological need. This makes the intervention rationale clear.
Example 3: Multi-Step Biochemical Pathway
TGF-β mediated collagen synthesis:
{
"@type": "CausalPathway",
"name": "TGF-β mediated collagen synthesis pathway",
"pathwaySteps": [
{
"@type": "CausalStep",
"stepNumber": 1,
"mechanism": "TGF-β binds to TGF-β receptor complex on fibroblast surface",
"result": "Receptor kinase domain phosphorylates SMAD2 and SMAD3 proteins"
},
{
"@type": "CausalStep",
"stepNumber": 2,
"mechanism": "Phosphorylated SMAD2/3 form complex with SMAD4",
"result": "SMAD complex translocates from cytoplasm into nucleus"
},
{
"@type": "CausalStep",
"stepNumber": 3,
"mechanism": "SMAD complex binds to regulatory regions of collagen genes",
"result": "Increased transcription of COL1A1, COL1A2, and COL3A1 genes"
}
]
}Why this works: Each step has a distinct mechanism (binding, complex formation, gene regulation) and each result feeds into the next step's context. The pathway reads as a coherent chain of causation.
Anti-Example: Confusing Mechanism and Result
Problematic:
{
"@type": "CausalStep",
"mechanism": "Increased inflammation",
"result": "Tissue damage from inflammatory mediators"
}Better:
{
"@type": "CausalStep",
"mechanism": "Activated macrophages release pro-inflammatory cytokines (TNF-α, IL-1β, IL-6)",
"result": "Local tissue inflammation with increased vascular permeability"
}Why the first version fails: "Increased inflammation" is a state, not an action. It doesn't tell you how inflammation occurs. The corrected version identifies the actors (macrophages), the action (release), and the specific molecules involved.
Implementation Notes
Relationship to schema.org
Schema.org has mechanismOfAction on Drug and DietarySupplement, but this is limited to pharmacological contexts. Health Schema's mechanism property is broader, applying to any causal step in any biological pathway—not just drug actions.
Validation
Standard schema.org validators will not recognise this property. This is expected for Health Schema extensions. The property is defined in the Health Schema context and will be correctly interpreted by systems that load this context.