diff --git a/lint b/lint
index f8ab2b6..cf21d5a 100755
--- a/lint
+++ b/lint
@@ -4,9 +4,9 @@ set -e
 cd $( dirname ${BASH_SOURCE[0]})
 . ./activate.sh
 echo Running ruff src
-ruff --fix src
+ruff check --fix src
 echo Running ruff tests
-ruff --fix tests
+ruff check --fix tests
 echo Running black src tests
 black src tests
 echo Running isort src tests
diff --git a/pyproject.toml b/pyproject.toml
index 6fe1d9b..bbb37bb 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -14,7 +14,7 @@ dependencies = [
     "wheel",
     "filelock",
     "semver",
-    "setuptools"
+    "setuptools",
 ]
 # Change this with the version number bump.
 version = "1.3.1"
diff --git a/src/isolated_environment/__init__.py b/src/isolated_environment/__init__.py
index 0e18775..6632cf5 100644
--- a/src/isolated_environment/__init__.py
+++ b/src/isolated_environment/__init__.py
@@ -10,14 +10,18 @@
 # the python interpreter.  On linux it will drop you into the
 # python interpreter and you will not be able to exit.
 def isolated_environment(
-    env_path: Union[Path, str], requirements: list[str] | None = None
+    env_path: Union[Path, str],
+    requirements: list[str] | None = None,
+    full_isolation: bool = False,
 ) -> dict[str, Any]:
     """Creates an isolated environment."""
     if isinstance(env_path, str):
         env_path = Path(env_path)  # type: ignore
     requirements = requirements or []
     reqs = Requirements(requirements)
-    iso_env = IsolatedEnvironment(env_path, reqs)
+    iso_env = IsolatedEnvironment(
+        env_path=env_path, requirements=reqs, full_isolation=full_isolation
+    )
     env = iso_env.environment()
     return env
 
@@ -26,6 +30,7 @@ def isolated_environment_run(
     env_path: Union[Path, str],
     requirements: list[str] | None,
     cmd_list: list[str],
+    full_isolation: bool = False,
     **kwargs: Any,
 ) -> CompletedProcess:
     """
@@ -40,7 +45,9 @@ def isolated_environment_run(
         env_path = Path(env_path)  # type: ignore
     requirements = requirements or []
     reqs = Requirements(requirements)
-    iso_env = IsolatedEnvironment(env_path, reqs)
+    iso_env = IsolatedEnvironment(
+        env_path=env_path, requirements=reqs, full_isolation=full_isolation
+    )
     iso_env.ensure_installed(reqs)
     cp = iso_env.run(cmd_list, **kwargs)
     return cp
diff --git a/src/isolated_environment/api.py b/src/isolated_environment/api.py
index 8b88a52..054e71a 100644
--- a/src/isolated_environment/api.py
+++ b/src/isolated_environment/api.py
@@ -14,6 +14,7 @@
 import warnings
 from contextlib import contextmanager
 from pathlib import Path
+from shutil import which
 from typing import Any, Iterator
 
 from filelock import FileLock
@@ -43,9 +44,34 @@ def _create_virtual_env(env_path: Path) -> Path:
     return env_path
 
 
-def _get_activated_environment(env_path: Path) -> dict[str, str]:
+def has_python_or_pip(path: str) -> bool:
+    """Returns True if python or pip is in the path."""
+    python = which("python", path=path) or which("python3", path=path)
+    pip = which("pip", path=path) or which("pip3", path=path)
+    return (python is not None) or (pip is not None)
+
+
+def _remove_python_paths_from_env(env: dict[str, str]) -> dict[str, str]:
+    """Removes PYTHONPATH from the environment."""
+    out_env = env.copy()
+    if "PYTHONPATH" in out_env:
+        del out_env["PYTHONPATH"]
+    path_list = out_env["PATH"].split(os.pathsep)
+
+    exported_path_list: list[str] = []
+    for p in path_list:
+        if not has_python_or_pip(p):
+            exported_path_list.append(p)
+    exported_path_list = [os.path.basename(sys.executable)] + exported_path_list
+    out_env["PATH"] = os.pathsep.join(exported_path_list)
+    return out_env
+
+
+def _get_activated_environment(env_path: Path, full_isolation: bool) -> dict[str, str]:
     """Gets the activate environment for the environment."""
     out_env = os.environ.copy()
+    if full_isolation:
+        out_env = _remove_python_paths_from_env(out_env)
     if sys.platform == "win32":
         out_env["PATH"] = str(env_path / "Scripts") + ";" + out_env["PATH"]
     else:
@@ -60,11 +86,11 @@ def _get_activated_environment(env_path: Path) -> dict[str, str]:
 
 
 def _pip_install(
-    env_path: Path, package: str, build_options: str | None = None
+    env_path: Path, package: str, build_options: str | None, full_isolation: bool
 ) -> None:
     """Installs a package in the virtual environment."""
     # Activate the environment and install packages
-    env = _get_activated_environment(env_path)
+    env = _get_activated_environment(env_path, full_isolation)
     cmd_list = ["pip", "install", package]
     if build_options:
         cmd_list.extend(build_options.split(" "))
@@ -85,15 +111,18 @@ class IsolatedEnvironment:
     """An isolated environment."""
 
     def __init__(
-        self, env_path: Path, requirements: Requirements | None = None
+        self,
+        env_path: Path,
+        requirements: Requirements | None = None,
+        full_isolation: bool = False,  # For absolute isolation, set to False
     ) -> None:
         self.env_path = env_path
+        self.full_isolation = full_isolation
         self.env_path.mkdir(parents=True, exist_ok=True)
         # file_lock is side-by-side with the environment.
         self.file_lock = FileLock(str(env_path) + ".lock")
         self.packages_json = env_path / "packages.json"
-        if requirements is not None:
-            self.ensure_installed(requirements)
+        self.ensure_installed(requirements or Requirements([]))
 
     def install_environment(self) -> None:
         """Installs the environment."""
@@ -141,7 +170,10 @@ def lock(self) -> Iterator[None]:
             self.file_lock.release()
 
     def pip_install(
-        self, package: str | list[str], build_options: str | None = None
+        self,
+        package: str | list[str],
+        build_options: str | None,
+        full_isolation: bool,
     ) -> None:
         """Installs a package in the virtual environment."""
         assert (
@@ -150,10 +182,10 @@ def pip_install(
         reqs = self._read_reqs()
         if isinstance(package, list):
             for p in package:
-                _pip_install(self.env_path, p, build_options)
+                _pip_install(self.env_path, p, build_options, full_isolation)
                 reqs.add(package)
         elif isinstance(package, str):
-            _pip_install(self.env_path, package, build_options)
+            _pip_install(self.env_path, package, build_options, full_isolation)
             reqs.add(package)
         else:
             raise TypeError(f"Unknown type for package: {type(package)}")
@@ -161,7 +193,7 @@ def pip_install(
 
     def environment(self) -> dict[str, str]:
         """Gets the activated environment, which should be applied to subprocess environments."""
-        return _get_activated_environment(self.env_path)
+        return _get_activated_environment(self.env_path, self.full_isolation)
 
     def run(self, cmd_list: list[str], **kwargs) -> subprocess.CompletedProcess:
         """Runs a command in the environment."""
@@ -186,6 +218,14 @@ def run(self, cmd_list: list[str], **kwargs) -> subprocess.CompletedProcess:
         text = kwargs.get("text", universal_newlines)
         if "text" in kwargs:
             del kwargs["text"]
+        scripts = "Scripts" if sys.platform == "win32" else "bin"
+        python_name = "python.exe" if sys.platform == "win32" else "python"
+        if cmd_list and (
+            cmd_list[0] == "python"
+            or cmd_list[0] == "python.exe"
+            or cmd_list[0] == "python3"
+        ):
+            cmd_list[0] = str(self.env_path / scripts / python_name)
         cp = subprocess.run(
             cmd_list,
             env=env,
@@ -248,7 +288,11 @@ def ensure_installed(self, reqs: Requirements) -> dict[str, Any]:
                 if req not in prev_reqs:
                     package_str = req.get_package_str()
                     build_options = req.build_options
-                    self.pip_install(package=package_str, build_options=build_options)
+                    self.pip_install(
+                        package=package_str,
+                        build_options=build_options,
+                        full_isolation=self.full_isolation,
+                    )
             self._write_reqs(reqs)
             return self.environment()
 
diff --git a/test b/test
index 66bf098..24de54b 100755
--- a/test
+++ b/test
@@ -3,4 +3,4 @@ set -e
 # cd to self bash script directory
 cd $( dirname ${BASH_SOURCE[0]})
 . ./activate.sh
-pytest
\ No newline at end of file
+pytest -n auto -v tests
\ No newline at end of file
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 70ab63a..2cf80a9 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -1,6 +1,7 @@
 """
 Unit test file.
 """
+
 import os
 import unittest
 
diff --git a/tests/test_data/inner.py b/tests/test_data/inner.py
new file mode 100644
index 0000000..d76fb3f
--- /dev/null
+++ b/tests/test_data/inner.py
@@ -0,0 +1,18 @@
+import sys
+
+try:
+    from isolated_environment import api
+
+    print(api)
+    print("Successfully imported IsolatedEnvironment")
+    # print the path to find the isolated_environment module
+    # print(api.__file__)
+    print(f"IsolatedEnvironment path: {api.__file__}")
+    # print out the python path
+    # print(sys.path)
+    # print out the python executable
+    print(f"Python executable: {sys.executable}")
+    sys.exit(0)
+except ImportError:
+    print("Failed to import IsolatedEnvironment")
+    sys.exit(1)
diff --git a/tests/test_full_isolation.py b/tests/test_full_isolation.py
new file mode 100644
index 0000000..8e82153
--- /dev/null
+++ b/tests/test_full_isolation.py
@@ -0,0 +1,49 @@
+"""
+Unit test file.
+"""
+
+import json
+import os
+import shutil
+import subprocess
+import unittest
+from pathlib import Path
+from tempfile import TemporaryDirectory
+from typing import Any
+
+from isolated_environment.api import IsolatedEnvironment
+
+HERE = Path(__file__).parent.absolute()
+TEST_DATA = HERE / "test_data"
+INNER_PY = TEST_DATA / "inner.py"
+
+assert INNER_PY.exists(), f"Missing: {INNER_PY}"
+
+
+def pretty(data: Any) -> str:
+    """Make JSON beautiful."""
+    return json.dumps(data, indent=4, sort_keys=True)
+
+
+class FullIoslationTester(unittest.TestCase):
+    """Main tester class."""
+
+    def test_ensure_installed(self) -> None:
+        """Tests that ensure_installed works."""
+        with TemporaryDirectory() as tmp_dir:
+            prev_dir = os.getcwd()
+            os.chdir(tmp_dir)
+            shutil.copy(INNER_PY, tmp_dir)
+            try:
+                iso_env = IsolatedEnvironment(
+                    Path(tmp_dir) / "venv", requirements=None, full_isolation=True
+                )
+                # now create an inner environment without the static-ffmpeg
+                cp: subprocess.CompletedProcess = iso_env.run(["python", "inner.py"])
+                self.assertEqual(1, cp.returncode)
+            finally:
+                os.chdir(prev_dir)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/test_iso_environment.py b/tests/test_iso_environment.py
index ca795b6..19dc90f 100644
--- a/tests/test_iso_environment.py
+++ b/tests/test_iso_environment.py
@@ -46,8 +46,9 @@ def test_ensure_installed(self) -> None:
             self.assertEqual(installed_reqs, reqs)
             try:
                 subprocess.check_output(
-                    ["static_ffmpeg", "--help"], env=env,
-                    shell=True  # shell=True is allowed only when NOT running python.
+                    ["static_ffmpeg", "--help"],
+                    env=env,
+                    shell=True,  # shell=True is allowed only when NOT running python.
                 )
             except subprocess.CalledProcessError as exc:
                 # doesn't fail on Windows, but it does on other platforms
diff --git a/tests/test_requirements.py b/tests/test_requirements.py
index 6582fd3..5a28d46 100644
--- a/tests/test_requirements.py
+++ b/tests/test_requirements.py
@@ -1,6 +1,7 @@
 """
 Unit test file.
 """
+
 import unittest
 
 from isolated_environment.requirements import Requirements
diff --git a/tests/test_run_py_file.py b/tests/test_run_py_file.py
index 538f341..c1c6496 100644
--- a/tests/test_run_py_file.py
+++ b/tests/test_run_py_file.py
@@ -51,8 +51,10 @@ def test_isolated_environment_run(self) -> None:
         with TemporaryDirectory() as tmp_dir:
             venv_path = Path(tmp_dir) / "venv"
             cp = isolated_environment_run(
-                env_path=venv_path, requirements=[], cmd_list=["python", str(RUN_PY)],
-                capture_output=True
+                env_path=venv_path,
+                requirements=[],
+                cmd_list=["python", str(RUN_PY)],
+                capture_output=True,
             )
             self.assertEqual(0, cp.returncode)
             self.assertEqual("Hello World!\n", cp.stdout)