diff --git a/product/problems.mdx b/product/problems.mdx
index 37c2c03..2c38545 100644
--- a/product/problems.mdx
+++ b/product/problems.mdx
@@ -15,6 +15,7 @@ Every problem opens with a plain-language **title and description** that Interfe
 
 - **The evidence behind it.** Every [piece of evidence](/concepts#evidence) that rolled up into this problem, linked so you can drill into specific occurrences.
 - **Who it affected.** How many users hit it and how often, and the [users](https://interfere.com/~/*/users) themselves, so you can gauge impact instead of guessing.
+- **First seen and last seen.** *First seen* is when Interfere recorded the earliest piece of evidence for this problem. It tells you whether the problem just appeared or has been running for a while. *Last seen* is the most recent occurrence, so you can tell whether it's still happening or has gone quiet. Together they bound the window the problem has been active. When a resolved problem returns as a [regression](/concepts#regression), *last seen* advances to the new occurrence and *first seen* stays put.
 
 ## The timeline