diff --git a/plugins/postcss-custom-properties/CHANGELOG.md b/plugins/postcss-custom-properties/CHANGELOG.md
index 4693432ee..ec10fd379 100644
--- a/plugins/postcss-custom-properties/CHANGELOG.md
+++ b/plugins/postcss-custom-properties/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changes to PostCSS Custom Properties
 
+### Unreleased
+
+- Improve plugin performance
+
 ### 12.1.10 (October 20, 2022)
 
 - Fix how `preserve: false` interacts with logic around duplicate code (see `12.1.9`).
diff --git a/plugins/postcss-custom-properties/src/lib/get-custom-properties-from-root.ts b/plugins/postcss-custom-properties/src/lib/get-custom-properties-from-root.ts
index e177478fa..1ea953d63 100644
--- a/plugins/postcss-custom-properties/src/lib/get-custom-properties-from-root.ts
+++ b/plugins/postcss-custom-properties/src/lib/get-custom-properties-from-root.ts
@@ -1,15 +1,18 @@
 import valuesParser from 'postcss-value-parser';
-import { isBlockIgnored } from './is-ignored';
+import { isBlockIgnored, isDeclarationIgnored } from './is-ignored';
 
 // return custom selectors from the css root, conditionally removing them
 export default function getCustomPropertiesFromRoot(root, opts): Map<string, valuesParser.ParsedValue> {
 	// initialize custom selectors
-	const customPropertiesFromHtmlElement: Map<string, valuesParser.ParsedValue> = new Map();
-	const customPropertiesFromRootPseudo: Map<string, valuesParser.ParsedValue> = new Map();
-	const out: Map<string, valuesParser.ParsedValue> = new Map();
+	const customPropertiesFromHtmlElement: Map<string, string> = new Map();
+	const customPropertiesFromRootPseudo: Map<string, string> = new Map();
 
 	// for each html or :root rule
 	root.nodes.slice().forEach(rule => {
+		if (isBlockIgnored(rule)) {
+			return;
+		}
+
 		const customPropertiesObject = isHtmlRule(rule)
 			? customPropertiesFromHtmlElement
 			: isRootRule(rule)
@@ -19,11 +22,11 @@ export default function getCustomPropertiesFromRoot(root, opts): Map<string, val
 		// for each custom property
 		if (customPropertiesObject) {
 			rule.nodes.slice().forEach(decl => {
-				if (decl.variable && !isBlockIgnored(decl)) {
+				if (decl.variable && !isDeclarationIgnored(decl)) {
 					const { prop } = decl;
 
 					// write the parsed value to the custom property
-					customPropertiesObject.set(prop, valuesParser(decl.value));
+					customPropertiesObject.set(prop, decl.value);
 
 					// conditionally remove the custom property declaration
 					if (!opts.preserve) {
@@ -33,18 +36,19 @@ export default function getCustomPropertiesFromRoot(root, opts): Map<string, val
 			});
 
 			// conditionally remove the empty html or :root rule
-			if (!opts.preserve && isEmptyParent(rule) && !isBlockIgnored(rule)) {
+			if (!opts.preserve && isEmptyParent(rule)) {
 				rule.remove();
 			}
 		}
 	});
 
+	const out: Map<string, valuesParser.ParsedValue> = new Map();
 	for (const [name, value] of customPropertiesFromHtmlElement.entries()) {
-		out.set(name, value);
+		out.set(name, valuesParser(value));
 	}
 
 	for (const [name, value] of customPropertiesFromRootPseudo.entries()) {
-		out.set(name, value);
+		out.set(name, valuesParser(value));
 	}
 
 	// return all custom properties, preferring :root properties over html properties
diff --git a/plugins/postcss-custom-properties/src/lib/is-ignored.ts b/plugins/postcss-custom-properties/src/lib/is-ignored.ts
index e1c5ccc5c..9c3842f76 100644
--- a/plugins/postcss-custom-properties/src/lib/is-ignored.ts
+++ b/plugins/postcss-custom-properties/src/lib/is-ignored.ts
@@ -1,20 +1,43 @@
-function isBlockIgnored(ruleOrDeclaration) {
-	const rule = ruleOrDeclaration.selector ?
-		ruleOrDeclaration : ruleOrDeclaration.parent;
+import type { Comment, Container, Declaration, Node } from 'postcss';
 
-	return /(!\s*)?postcss-custom-properties:\s*off\b/i.test(rule.toString());
+const blockRegExp = /(!\s*)?postcss-custom-properties:\s*off\b/i;
+
+const blockIgnoredCache = new WeakMap();
+
+function isBlockIgnored(container: Container) {
+	if (!container || !container.nodes) {
+		return false;
+	}
+
+	if (blockIgnoredCache.has(container)) {
+		return blockIgnoredCache.get(container);
+	}
+
+	const result = container.some((child) => isIgnoreComment(child, blockRegExp));
+	blockIgnoredCache.set(container, result);
+
+	return result;
 }
 
-function isRuleIgnored(rule) {
-	const previous = rule.prev();
+const declarationRegExp = /(!\s*)?postcss-custom-properties:\s*ignore\s+next\b/i;
+
+function isDeclarationIgnored(decl: Declaration) {
+	if (!decl) {
+		return false;
+	}
+
+	if (isBlockIgnored(decl.parent)) {
+		return true;
+	}
+
+	return isIgnoreComment(decl.prev(), declarationRegExp);
+}
 
-	return Boolean(isBlockIgnored(rule) ||
-		previous &&
-		previous.type === 'comment' &&
-		/(!\s*)?postcss-custom-properties:\s*ignore\s+next\b/i.test(previous.text));
+function isIgnoreComment(node: Node, regexp: RegExp) {
+	return node && node.type === 'comment' && regexp.test((node as Comment).text);
 }
 
 export {
 	isBlockIgnored,
-	isRuleIgnored,
+	isDeclarationIgnored,
 };
diff --git a/plugins/postcss-custom-properties/src/lib/transform-properties.ts b/plugins/postcss-custom-properties/src/lib/transform-properties.ts
index da2a8147a..f0ac25055 100644
--- a/plugins/postcss-custom-properties/src/lib/transform-properties.ts
+++ b/plugins/postcss-custom-properties/src/lib/transform-properties.ts
@@ -1,11 +1,11 @@
 import valuesParser from 'postcss-value-parser';
 import transformValueAST from './transform-value-ast';
-import { isRuleIgnored } from './is-ignored';
 import { Declaration } from 'postcss';
+import { isDeclarationIgnored } from './is-ignored';
 
 // transform custom pseudo selectors with custom selectors
 export default (decl, customProperties, opts) => {
-	if (isTransformableDecl(decl) && !isRuleIgnored(decl)) {
+	if (isTransformableDecl(decl) && !isDeclarationIgnored(decl)) {
 		const originalValue = decl.value;
 		const valueAST = valuesParser(originalValue);
 		let value = transformValueAST(valueAST, customProperties);