What Is a Death Cap Mushroom?

It is one of the most dangerous mushrooms. CDC's MMWR says amatoxin-containing mushrooms account for more than 90 percent of mushroom poisoning deaths worldwide, and that even with medical intervention, amatoxin mushroom poisoning is fatal in 10 to 20 percent of patients. It says the toxins, amanitins, are heat stable and not inactivated by cooking, and once eaten are absorbed from the gut and taken up by liver cells, where they halt protein synthesis and cause cell death.

The early recovery can be false. The California Department of Public Health says stomach symptoms resembling viral gastroenteritis can start within 6 to 24 hours and typically resolve within 24 hours, but that this improvement can create a false impression of recovery, because patients may still progress to potentially fatal liver damage within 48 to 96 hours after eating the mushrooms.

California has seen repeated outbreaks. The state health department says death caps are widely established in parts of California, particularly next to oaks and other hardwoods, including pines, and that fall and winter rains create ideal growing conditions. CDC's MMWR reported that over 2 weeks in December 2016 the California Poison Control System investigated 14 suspected death cap ingestions in five northern California counties, and that 3 of the patients required liver transplants because of irreversible liver failure. It also reported that from November 2025 to March 2026 an outbreak of 39 amatoxin mushroom poisoning cases in northern California resulted in three liver transplants and four deaths.

San Luis Obispo County's public health department advises seeking medical care right away and calling the California Poison Control Hotline at 1-800-222-1222. CDC's MMWR says there are no standardized treatment regimens and no FDA-approved therapies for amatoxin poisoning, and that aggressive IV hydration is recommended because amatoxin is eliminated by the kidneys.