diff --git a/launch.py b/launch.py
index 8f7e27d4..085d02cc 100644
--- a/launch.py
+++ b/launch.py
@@ -2,10 +2,11 @@ import os
 import sys
 import platform
 
-from modules.launch_util import commit_hash, fooocus_tag, is_installed, run, python, run_pip, repo_dir, git_clone
+from modules.launch_util import commit_hash, fooocus_tag, is_installed, run, python, \
+    run_pip, repo_dir, git_clone, requirements_met
 
 
-REINSTALL_ALL = True
+REINSTALL_ALL = False
 
 
 def prepare_environment():
@@ -42,6 +43,10 @@ def prepare_environment():
         elif platform.system() == "Linux":
             run_pip(f"install -U -I --no-deps {xformers_package}", "xformers")
 
+    if REINSTALL_ALL or not requirements_met(requirements_file):
+        run_pip(f"install -r \"{requirements_file}\"", "requirements")
+
+    return
 
 
 prepare_environment()
diff --git a/modules/launch_util.py b/modules/launch_util.py
index a14e8094..63f329b3 100644
--- a/modules/launch_util.py
+++ b/modules/launch_util.py
@@ -2,6 +2,7 @@ import os
 import importlib
 import subprocess
 import sys
+import re
 
 from functools import lru_cache
 
@@ -95,3 +96,41 @@ def run(command, desc=None, errdesc=None, custom_env=None, live: bool = default_
 def run_pip(command, desc=None, live=default_command_live):
     index_url_line = f' --index-url {index_url}' if index_url != '' else ''
     return run(f'"{python}" -m pip {command} --prefer-binary{index_url_line}', desc=f"Installing {desc}", errdesc=f"Couldn't install {desc}", live=live)
+
+
+re_requirement = re.compile(r"\s*([-_a-zA-Z0-9]+)\s*(?:==\s*([-+_.a-zA-Z0-9]+))?\s*")
+
+
+def requirements_met(requirements_file):
+    """
+    Does a simple parse of a requirements.txt file to determine if all rerqirements in it
+    are already installed. Returns True if so, False if not installed or parsing fails.
+    """
+
+    import importlib.metadata
+    import packaging.version
+
+    with open(requirements_file, "r", encoding="utf8") as file:
+        for line in file:
+            if line.strip() == "":
+                continue
+
+            m = re.match(re_requirement, line)
+            if m is None:
+                return False
+
+            package = m.group(1).strip()
+            version_required = (m.group(2) or "").strip()
+
+            if version_required == "":
+                continue
+
+            try:
+                version_installed = importlib.metadata.version(package)
+            except Exception:
+                return False
+
+            if packaging.version.parse(version_required) != packaging.version.parse(version_installed):
+                return False
+
+    return True