What Happens When Job Duties Aggravate a Pre-Existing Condition?

 Posted on June 05, 2026 in Workers' Compensation

Workers with a bad back, a worn-out knee, or an old shoulder injury often assume they cannot file a workers' compensation claim when the job makes their injury worse. That assumption is wrong, and it costs people real money. In California, a pre-existing condition does not disqualify your workers' comp claim, and what counts is whether your job made your condition worse. If it did, you have a claim. A Gilroy, CA workers' compensation attorney can help you understand what you are owed in 2026 and how to protect your right to workers' compensation benefits.

Does Having a Pre-Existing Condition Disqualify You from Workers' Comp in California?

A prior health condition does not mean you cannot file for workers' comp. California law protects workers whose jobs worsen pre-existing conditions. Under California Labor Code § 3208, a compensable injury includes an injury or disease arising out of and occurring in the course of employment. California workers' compensation benefits may be available when work activities aggravate or accelerate a pre-existing condition.

Claims adjusters look at whether your job caused your current condition, fully or in part. If your records show your pre-existing condition got worse because of your work, you can seek benefits for that worsening. Consider a worker with a prior knee injury who spent years kneeling on concrete as a farm worker or construction laborer. That worker may have a valid claim even though the knee was already damaged. Your condition does not have to have been healthy before you started the job.

What Should You Do When Your Pre-Existing Condition Gets Worse at Work?

Many workers wait too long to take action after noticing a worsening condition. If you think your job is making your condition worse, take these steps:

• Report the worsening to your employer in writing and keep a copy for your records.
• See a doctor and describe exactly how your job duties affect your condition.
• Write down the physical tasks your job requires, how often you do them, and how your symptoms have changed.
• Ask your doctor to note in your records when your symptoms changed and what caused them.

Under California Labor Code § 5400, you must notify your employer within 30 days of a work injury, and waiting too long may give the insurer a reason to deny your claim.

How Does California's Apportionment Law Reduce Benefits When You Have a Prior Condition?

Even when a claim is accepted, your permanent disability benefits may still be reduced. This happens through a process called apportionment. Under California Labor Code § 4663, the doctor who examines you must state what percentage of your permanent disability came from your job versus other causes. Your benefits are then based only on the work-related share.

Here is a simple example. A doctor finds that 60 percent of your back disability comes from a prior condition and 40 percent comes from your job. Your benefits are calculated only on that 40 percent. Apportionment does not wipe out your claim, but it can reduce the payout.

The doctor's report drives this outcome. Under § 4663, that report must include an apportionment finding to be complete. An insurer cannot simply claim your condition is mostly pre-existing without a solid medical opinion to support it. However, if the doctor's reasoning is vague or unsupported by evidence, it can be challenged.

What Evidence Do You Need to Prove a Work Aggravation Claim in California?

The U.S. Bureau of Labor Statistics reported more than 502,000 musculoskeletal disorder cases causing days away from work over a recent two-year period. These injuries are common in physically demanding jobs, and some workers may have had prior wear or old injuries before their symptoms got worse. If your situation sounds similar, you are not in unusual territory.

Strong evidence in aggravation claim cases includes medical records that show your condition before and after your job duties changed, a clear doctor's opinion linking your work to the worsening, and a record of what your job required physically. A timeline connecting changes in your symptoms to changes in your workload also helps your case.

Insurers sometimes try to push apportionment beyond what the law allows. They may claim that your disability is due to age, weight, or lifestyle rather than your job, and as a response, California courts have placed limits on this approach. An apportionment opinion must be based on solid medical evidence and clear reasoning, and a speculative report can be challenged and thrown out.

Be upfront with your doctor about any prior injuries or diagnoses. A doctor who knows your full history can write a report that correctly ties new damage to your job, and that report is one of the most powerful tools in your case. Workers who try to hide a prior condition often find that insurers uncover it anyway and use it to cast doubt on everything they have claimed.

Contact a Gilroy, CA Workers' Compensation Attorney About Your Pre-Existing Condition Claim

If your job has made an existing health problem worse, you may be owed benefits even if that condition came before your current employment. The Santa Clara County, CA work injury lawyer at Raul Martinez Injury Law Firm brings more than 15 years of legal experience to workers' comp cases throughout the area. Call 408-848-1113 to schedule a free consultation today.