Causation vs. aggravation theories

Two distinct legal theories operate under the secondary umbrella. Both are valid. Many veterans only know about the first.

Causation theory

Your service-connected condition CAUSED the new condition. The new condition did not exist before the SC primary, or its onset is attributable to the SC primary or its treatment.

Example: Service-connected diabetes caused peripheral neuropathy.

Aggravation theory

Your service-connected condition AGGRAVATED a pre-existing or otherwise non-SC condition — made it worse than its natural progression. The VA must compensate you for the difference between baseline severity and current severity.

Example: You had mild migraines before service. Service-connected PTSD aggravated them to chronic, prostrating attacks. You are compensated for the worsening attributable to PTSD.

Pro tip

Aggravation is widely underused because veterans assume “I had this before I deployed” disqualifies them. It doesn’t. If you can show baseline severity (pre-SC condition) and current severity (post-SC condition), the difference is compensable. A skilled nexus letter writer can frame this clearly.

Cover both bases

Have your nexus letter writer address BOTH causation AND aggravation, even if only one applies. If VA rejects causation, they may still grant on aggravation. Use phrasing like:

“It is at least as likely as not that the veteran’s [condition] was either caused by OR aggravated beyond its natural progression by the service-connected [primary].”

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