diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index c8f66bd459f69..7e3eaf8665d39 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -79,18 +79,6 @@ then
   export HOMEBREW_GEM_PATH="$GEM_PATH"
 fi
 
-# Users may have these set, pointing the system Ruby
-# at non-system gem paths
-unset GEM_HOME
-unset GEM_PATH
-
-# Users may have this set, injecting arbitrary environment changes into
-# bash processes inside builds
-unset BASH_ENV
-
-# Users may have this set, breaking grep's output.
-unset GREP_OPTIONS
-
 HOMEBREW_SYSTEM="$(uname -s)"
 case "$HOMEBREW_SYSTEM" in
   Darwin) HOMEBREW_MACOS="1" ;;
diff --git a/Library/Homebrew/cmd/update.sh b/Library/Homebrew/cmd/update.sh
index 609e4094a9904..7477845274cf3 100644
--- a/Library/Homebrew/cmd/update.sh
+++ b/Library/Homebrew/cmd/update.sh
@@ -410,9 +410,6 @@ EOS
     QUIET_ARGS=()
   fi
 
-  # ensure GIT_CONFIG is unset as we need to operate on .git/config
-  unset GIT_CONFIG
-
   # only allow one instance of brew update
   lock update
 
diff --git a/Library/Homebrew/diagnostic.rb b/Library/Homebrew/diagnostic.rb
index 61f9b53a359e7..41deaf23ea5d7 100644
--- a/Library/Homebrew/diagnostic.rb
+++ b/Library/Homebrew/diagnostic.rb
@@ -1017,16 +1017,6 @@ def check_for_unlinked_but_not_keg_only
         EOS
       end
 
-      def check_for_old_env_vars
-        return unless ENV["HOMEBREW_KEEP_INFO"]
-
-        <<~EOS
-          `HOMEBREW_KEEP_INFO` is no longer used
-          info files are no longer deleted by default; you may
-          remove this environment variable.
-        EOS
-      end
-
       def check_for_pth_support
         homebrew_site_packages = Language::Python.homebrew_site_packages
         return unless homebrew_site_packages.directory?
diff --git a/Library/Homebrew/extend/os/mac/diagnostic.rb b/Library/Homebrew/extend/os/mac/diagnostic.rb
index f86155f2e51fe..bb89b2367f7fd 100644
--- a/Library/Homebrew/extend/os/mac/diagnostic.rb
+++ b/Library/Homebrew/extend/os/mac/diagnostic.rb
@@ -262,19 +262,6 @@ def check_for_bad_curl
         EOS
       end
 
-      def check_for_unsupported_curl_vars
-        # Support for SSL_CERT_DIR seemed to be removed in the 10.10.5 update.
-        return unless MacOS.version >= :yosemite
-        return if ENV["SSL_CERT_DIR"].nil?
-
-        <<~EOS
-          SSL_CERT_DIR support was removed from Apple's curl.
-          If fetching formulae fails you should:
-            unset SSL_CERT_DIR
-          and remove it from #{Utils::Shell.profile} if present.
-        EOS
-      end
-
       def check_xcode_license_approved
         # If the user installs Xcode-only, they have to approve the
         # license or no "xc*" tool will work.
diff --git a/Library/Homebrew/test/os/mac/diagnostic_spec.rb b/Library/Homebrew/test/os/mac/diagnostic_spec.rb
index 83d95c2ef1734..f04652a93687b 100644
--- a/Library/Homebrew/test/os/mac/diagnostic_spec.rb
+++ b/Library/Homebrew/test/os/mac/diagnostic_spec.rb
@@ -15,14 +15,6 @@
       .to match("We do not provide support for this pre-release version.")
   end
 
-  specify "#check_for_unsupported_curl_vars" do
-    allow(MacOS).to receive(:version).and_return(OS::Mac::Version.new("10.10"))
-    ENV["SSL_CERT_DIR"] = "/some/path"
-
-    expect(subject.check_for_unsupported_curl_vars)
-      .to match("SSL_CERT_DIR support was removed from Apple's curl.")
-  end
-
   specify "#check_for_beta_xquartz" do
     allow(MacOS::XQuartz).to receive(:version).and_return("2.7.10_beta2")