What Is Concurrent Causation — and Why Does It Matter?

Concurrent causation is a concept that arises when two or more perils — one covered by your policy and one excluded — act together to produce a single, indivisible loss. Under the traditional concurrent causation doctrine, courts generally held that if a covered peril was part of the causal chain, the entire claim should be paid. This was considered the fair, policyholder-friendly standard.

For example, imagine floodwaters weaken a riverbank, causing a landslide that damages your parked vehicle. The landslide (an excluded peril) and the flood (also often excluded) combine to total your car. But what if a covered peril like wind or collision was also involved? That's where things get complicated — and that's exactly where the anti-concurrent causation clause enters the picture.

How the Anti-Concurrent Causation Clause Works to Deny Claims

The anti-concurrent causation (ACC) clause is a provision insurers include in policy exclusion sections to override the pro-policyholder concurrent causation doctrine. It states that a loss is excluded if an excluded peril contributed to the damage in any way, in any sequence, or at any time — even if a covered peril also played a role.

The language typically reads something like:

"We will not pay for loss or damage caused directly or indirectly by [excluded peril]. Such loss is excluded regardless of any other cause or event that contributes concurrently or in any sequence to the loss."

This is a sweeping clause. It doesn't require the excluded peril to be the primary cause — it only requires that the excluded peril be somewhere in the chain of events. The result: insurers can deny the entire claim, including the covered portion, without having to separate or apportion the two causes of damage.

Real-World ACC Claim Denial Examples

Understanding the ACC clause in abstract terms is helpful, but seeing how it plays out in actual claim scenarios makes the risk much more concrete. If your claim has ever been denied, learning about common claim denial reasons and how to appeal can give you a solid starting point.

Example 1: Flood + Collision

You're driving during a flash flood and hydroplane off the road, striking a guardrail. Your vehicle sustains collision damage (a covered peril under your collision coverage) and flood damage (an excluded peril under most standard auto policies). When you file your claim, the insurer discovers that floodwater entered the engine compartment and contributed to the total loss.

Result with ACC clause: The insurer denies the entire claim — including the collision portion — because flood, an excluded peril, contributed to the loss "in any sequence."

Example 2: Earthquake + Vandalism

An earthquake causes a retaining wall to collapse onto your vehicle (excluded peril). During the chaos, vandals also break your windows and slash your tires (covered under comprehensive). You file a comprehensive claim for the vandalism.

Result with ACC clause: If your policy excludes earthquake damage and contains an ACC clause, the insurer may deny the vandalism portion entirely because the earthquake — an excluded peril — "contributed concurrently to the loss."

Example 3: Mechanical Breakdown + Collision

Your brakes fail (mechanical breakdown — often excluded), causing you to rear-end another vehicle. The collision caused the physical damage.

Result with ACC clause: In policies where mechanical or electrical failure is excluded and ACC language is present, the insurer may attempt to deny coverage by arguing that the excluded mechanical failure was a contributing concurrent cause.

States That Limit or Prohibit ACC Clauses

Not all states allow insurers to use anti-concurrent causation clauses freely. The enforceability of ACC provisions varies significantly depending on where you live. This is one reason why understanding your state-specific car insurance claim deadlines and protections is so important.

In California and Washington, the efficient proximate cause doctrine is the standard. Under this rule, courts look at which peril was the dominant or primary cause of the loss — and if that peril is covered, the claim must be paid regardless of secondary excluded causes. This makes ACC clauses largely unenforceable in those states.

How to Find ACC Language in Your Policy

ACC clauses are intentionally buried in the exclusions section of your policy. Here's how to locate them:

1. Open your policy's Declarations or Full Policy Document — usually available via your insurer's online portal or by request.
2. Navigate to the "Exclusions" or "Causes of Loss" section — this is where excluded perils are listed.
3. Search for these trigger phrases:
   • "concurrently"
   • "in any sequence"
   • "regardless of any other cause"
   • "directly or indirectly"
   • "whether or not combined with"
4. Look at the preamble to exclusions — many ACC clauses appear as a blanket statement that applies to all listed exclusions, not just one.

If you find language stating the exclusion applies "regardless of any other cause or event that contributes concurrently or in any sequence to the loss" — that is a classic ACC clause.

If you can't find this language, your policy may default to the pro-policyholder concurrent causation doctrine. However, you should confirm this interpretation with an insurance attorney or licensed public adjuster.

How to Dispute an ACC-Based Claim Denial

If your claim has been denied citing the anti-concurrent causation clause, you have options. The process requires persistence, documentation, and in many cases professional help. Understanding your rights when it comes to disputing your car insurance claim outcome through the appraisal clause can also be a valuable tool in your arsenal.

Step 1: Request the Full Denial Letter

Demand a written denial letter that specifically cites the exact policy language used to deny your claim. Vague denials are harder for insurers to defend.

Step 2: Document Each Cause of Loss Separately

Hire an independent engineer, mechanic, or damage assessor to provide a written report attributing specific damage to specific causes. If flood caused engine damage but the collision caused frame damage, having that clearly separated gives you leverage. This type of documentation is the same foundation used in car insurance damage assessments after accidents.

Step 3: Challenge ACC Enforceability in Your State

Review your state's rules. If you're in California, Washington, or another state with efficient proximate cause protections, cite those laws directly in your appeal. Reference the specific court precedents that make ACC clauses unenforceable in your jurisdiction.

Step 4: File a Formal Appeal with Your Insurer

Submit a written appeal with supporting documentation. Include:

• A clear timeline of events showing the sequence of causes
• Independent expert reports
• Your state's legal standard on concurrent causation
• The argument that the covered peril was the efficient proximate cause

Step 5: File a Complaint with Your State Insurance Department

If the insurer refuses to reconsider, file a formal complaint with your state's Department of Insurance. Regulators take bad-faith denial patterns seriously. You can also escalate to understanding what to do when your insurance payout isn't enough.

Step 6: Consult an Insurance Attorney or Public Adjuster

For large claim amounts, retaining a licensed public adjuster or bad-faith insurance attorney can make a significant difference. Attorneys who specialize in insurance disputes understand how to argue concurrent causation cases and can shift the burden of proof back to the insurer.

Frequently Asked Questions

Does the anti-concurrent causation clause apply to all car insurance policies?

Not all auto insurance policies contain an ACC clause. It is more commonly found in homeowners and commercial property policies, but many standard personal auto policies do include exclusion language that mirrors ACC intent — particularly for flood, earthquake, and mechanical breakdown exclusions. Always read your full policy exclusions section, not just the coverage summary.

Can an insurer use the ACC clause to deny a collision claim caused by flooding?

Yes — in states where ACC clauses are enforceable, an insurer can deny a collision-related claim if floodwater also contributed to the vehicle's damage. The insurer does not need to prove flood was the primary cause, only that it contributed "in any sequence." This is why comprehensive and flood-specific coverage (like through the NFIP for vehicles) matters, and why understanding how hurricane coverage works for car insurance is critical if you live in a flood-prone area.

What is the difference between the ACC clause and the efficient proximate cause doctrine?

The efficient proximate cause doctrine asks: what was the dominant cause of the loss? If that dominant cause is covered, the whole claim is covered. The ACC clause eliminates this analysis entirely — it says that if any excluded peril contributed to the loss, the whole claim is denied. States like California and Washington apply the efficient proximate cause doctrine, which makes ACC clauses largely unenforceable there.

How can I protect myself from an ACC clause denial before a loss happens?

The best protection is thorough coverage. Purchase comprehensive auto coverage that includes as many perils as possible, minimizing the chance that any contributing cause is excluded. Review your policy exclusions annually, ask your agent about ACC language specifically, and consider adding endorsements for flood or earthquake if you live in high-risk areas. If you're unsure what coverages matter most, learning how to file a car insurance claim step-by-step can help you understand what's actually triggered when you make a claim.

Is an ACC-based claim denial considered bad faith insurance?

In some states and under specific circumstances, yes. If an insurer applies an ACC clause to deny a clearly covered loss or invokes the clause in a state where it is legally unenforceable, that could rise to the level of bad faith insurance conduct. Filing a complaint with your state's Department of Insurance and consulting with an attorney experienced in insurance bad faith is the right course of action in those situations.