diff --git a/CHANGES/5416.bug b/CHANGES/5416.bug
new file mode 100644
index 0000000000..cd1aaf0672
--- /dev/null
+++ b/CHANGES/5416.bug
@@ -0,0 +1 @@
+Collection documentation: process markup in deprecation messages.
diff --git a/src/components/render-plugin-doc.tsx b/src/components/render-plugin-doc.tsx
index c77fc3a8da..c7442ecc09 100644
--- a/src/components/render-plugin-doc.tsx
+++ b/src/components/render-plugin-doc.tsx
@@ -429,13 +429,15 @@ export class RenderPluginDoc extends Component<IProps, IState> {
 
         <div>
           <b>{t`Why:`}</b>{' '}
-          {deprecated.why ? doc.deprecated.why : t`No reason specified.`}
+          {deprecated.why
+            ? this.applyDocFormatters(doc.deprecated.why)
+            : t`No reason specified.`}
         </div>
 
         <div>
           <b>{t`Alternative:`}</b>{' '}
           {deprecated.alternative
-            ? doc.deprecated.alternative
+            ? this.applyDocFormatters(doc.deprecated.alternative)
             : t`No alternatives specified.`}
         </div>
       </>