diff --git a/api/src/services/quality_metrics_service.py b/api/src/services/quality_metrics_service.py
index c6e4926..34a3db9 100644
--- a/api/src/services/quality_metrics_service.py
+++ b/api/src/services/quality_metrics_service.py
@@ -354,6 +354,9 @@ class QualityMetricsService:
         return buffer.getvalue().encode("utf-8-sig"), "text/csv; charset=utf-8", "csv"
 
 
+_FORMULA_PREFIXES = ("=", "+", "-", "@", "\t", "\r")
+
+
 def _cell(value: Any) -> Any:
     """Значение ячейки CSV: перечисления — их значение, даты — ISO, булевы — true/false."""
     if isinstance(value, bool):
@@ -362,4 +365,6 @@ def _cell(value: Any) -> Any:
         return value.value
     if isinstance(value, datetime | date):
         return value.isoformat()
+    if isinstance(value, str) and value.startswith(_FORMULA_PREFIXES):
+        return "'" + value  # защита от CSV-инъекции формул в Excel
     return value
diff --git a/api/tests/test_api_quality_metrics.py b/api/tests/test_api_quality_metrics.py
index e37547d..7d3f3a2 100644
--- a/api/tests/test_api_quality_metrics.py
+++ b/api/tests/test_api_quality_metrics.py
@@ -30,7 +30,7 @@ from src.models.enums import (
 )
 from src.repositories.quality_facts import insert_failure_fact, insert_intake_fact, insert_outcome_fact
 from src.repositories.users import UserWithAccess
-from src.services.quality_metrics_service import EXPORT_COLUMNS
+from src.services.quality_metrics_service import EXPORT_COLUMNS, _cell
 from tests.conftest import AuthClientFactory
 
 HTTP_OK, HTTP_FORBIDDEN, HTTP_UNPROCESSABLE = 200, 403, 422
@@ -322,3 +322,15 @@ async def test_quality_metrics_export(auth_client: AuthClientFactory, seeded: As
     assert rows[0]["is_scan"] == "true"
     as_json = await client.get(f"{BASE}/export", params={"format": "json", "date_from": "2026-11-01"})
     assert len(as_json.json()) == 2  # noqa: PLR2004
+
+
+@pytest.mark.parametrize("prefix", ["=", "+", "-", "@", "\t", "\r"])
+def test_csv_cell_escapes_formula_strings(prefix: str) -> None:
+    assert _cell(f"{prefix}SUM(A1)") == f"'{prefix}SUM(A1)"
+
+
+def test_csv_cell_keeps_non_strings_and_plain_strings() -> None:
+    assert _cell(-5) == -5  # noqa: PLR2004
+    assert _cell("ООО Альфа") == "ООО Альфа"
+    assert _cell(datetime.date(2026, 11, 1)) == "2026-11-01"
+    assert _cell(True) == "true"