diff --git a/homeassistant/helpers/trigger.py b/homeassistant/helpers/trigger.py
index b89ec78aaa8..1665212d711 100644
--- a/homeassistant/helpers/trigger.py
+++ b/homeassistant/helpers/trigger.py
@@ -594,7 +594,8 @@ async def async_get_all_descriptions(
                 _load_triggers_files, hass, integrations
             )
 
-    # Add missing descriptions to the cache
+    # Make a copy of the old cache and add missing descriptions to it
+    new_descriptions_cache = descriptions_cache.copy()
     for missing_trigger in missing_triggers:
         domain = triggers[missing_trigger]
 
@@ -607,6 +608,7 @@ async def async_get_all_descriptions(
 
         description = {"fields": yaml_description.get("fields", {})}
 
-        descriptions_cache[missing_trigger] = description
+        new_descriptions_cache[missing_trigger] = description
 
-    return descriptions_cache
+    hass.data[TRIGGER_DESCRIPTION_CACHE] = new_descriptions_cache
+    return new_descriptions_cache
diff --git a/tests/components/websocket_api/test_commands.py b/tests/components/websocket_api/test_commands.py
index fba7eebd537..71f0ffb5941 100644
--- a/tests/components/websocket_api/test_commands.py
+++ b/tests/components/websocket_api/test_commands.py
@@ -17,6 +17,9 @@ from homeassistant.components.websocket_api.auth import (
     TYPE_AUTH_OK,
     TYPE_AUTH_REQUIRED,
 )
+from homeassistant.components.websocket_api.commands import (
+    ALL_TRIGGER_DESCRIPTIONS_JSON_CACHE,
+)
 from homeassistant.components.websocket_api.const import FEATURE_COALESCE_MESSAGES, URL
 from homeassistant.config_entries import ConfigEntryState
 from homeassistant.const import SIGNAL_BOOTSTRAP_INTEGRATIONS
@@ -685,6 +688,8 @@ async def test_subscribe_triggers(
     assert await async_setup_component(hass, "system_health", {})
     await hass.async_block_till_done()
 
+    assert ALL_TRIGGER_DESCRIPTIONS_JSON_CACHE not in hass.data
+
     await websocket_client.send_json_auto_id({"type": "trigger_platforms/subscribe"})
 
     # Test start subscription with initial event
@@ -693,6 +698,8 @@ async def test_subscribe_triggers(
     msg = await websocket_client.receive_json()
     assert msg == {"event": {"sun": {"fields": {}}}, "id": 1, "type": "event"}
 
+    old_cache = hass.data[ALL_TRIGGER_DESCRIPTIONS_JSON_CACHE]
+
     # Test we receive an event when a new platform is loaded
     assert await async_setup_component(hass, "tag", {})
     msg = await websocket_client.receive_json()
@@ -702,6 +709,35 @@ async def test_subscribe_triggers(
         "type": "event",
     }
 
+    # Initiate a second subscription to check the cache is updated because of the new
+    # trigger
+    await websocket_client.send_json_auto_id({"type": "trigger_platforms/subscribe"})
+    msg = await websocket_client.receive_json()
+    assert msg == {"id": 2, "result": None, "success": True, "type": "result"}
+    msg = await websocket_client.receive_json()
+    assert msg == {
+        "event": {"sun": {"fields": {}}, "tag": {"fields": {}}},
+        "id": 2,
+        "type": "event",
+    }
+
+    assert hass.data[ALL_TRIGGER_DESCRIPTIONS_JSON_CACHE] is not old_cache
+
+    # Initiate a third subscription to check the cache is not updated because no new
+    # trigger was added
+    old_cache = hass.data[ALL_TRIGGER_DESCRIPTIONS_JSON_CACHE]
+    await websocket_client.send_json_auto_id({"type": "trigger_platforms/subscribe"})
+    msg = await websocket_client.receive_json()
+    assert msg == {"id": 3, "result": None, "success": True, "type": "result"}
+    msg = await websocket_client.receive_json()
+    assert msg == {
+        "event": {"sun": {"fields": {}}, "tag": {"fields": {}}},
+        "id": 3,
+        "type": "event",
+    }
+
+    assert hass.data[ALL_TRIGGER_DESCRIPTIONS_JSON_CACHE] is old_cache
+
 
 async def test_get_config(
     hass: HomeAssistant, websocket_client: MockHAClientWebSocket