diff --git a/.changeset/orange-buttons-bow.md b/.changeset/orange-buttons-bow.md
new file mode 100644
index 000000000..54a912b9a
--- /dev/null
+++ b/.changeset/orange-buttons-bow.md
@@ -0,0 +1,8 @@
+---
+'@emotion/cache': patch
+---
+
+author: @danieldelcore
+author: @mitchellhamilton
+
+Fixed moving of client-side inserted style tags from Emotion 10 when intending to hydrate Emotion 11 styles resulting in losing styles in production
diff --git a/packages/cache/__tests__/hydration.js b/packages/cache/__tests__/hydration.js
index 2119d48f2..132f26237 100644
--- a/packages/cache/__tests__/hydration.js
+++ b/packages/cache/__tests__/hydration.js
@@ -35,3 +35,149 @@ test('rehydrated styles to head can be flushed', () => {
   cache.sheet.flush()
   expect(document.documentElement).toMatchSnapshot()
 })
+
+test('flushing rehydrated styles in the head only affect styles matching the cache key', () => {
+  safeQuerySelector('head').innerHTML = [
+    '<style data-emotion="emo 1lrxbo5">.emo-1lrxbo5{color:hotpink;}</style>',
+    '<style data-emotion="css qweqwee">.css-qweqwee{color:red;}</style>'
+  ].join('')
+
+  // this moves emotion style tags at initialization time
+  jest.resetModules()
+  require('@emotion/react')
+
+  const cache = createCache({ key: 'emo' })
+  expect(document.documentElement).toMatchInlineSnapshot(`
+    <html>
+      <head>
+        <style
+          data-emotion="css qweqwee"
+          data-s=""
+        >
+          .css-qweqwee{color:red;}
+        </style>
+        <style
+          data-emotion="emo 1lrxbo5"
+          data-s=""
+        >
+          .emo-1lrxbo5{color:hotpink;}
+        </style>
+      </head>
+      <body />
+    </html>
+  `)
+
+  cache.sheet.flush()
+  expect(document.documentElement).toMatchInlineSnapshot(`
+    <html>
+      <head>
+        <style
+          data-emotion="css qweqwee"
+          data-s=""
+        >
+          .css-qweqwee{color:red;}
+        </style>
+      </head>
+      <body />
+    </html>
+  `)
+})
+
+test('should only hydrate style elements matching the cache key', () => {
+  let css = `color:hotpink;`
+  let hash = hashString(css)
+
+  safeQuerySelector(
+    'body'
+  ).innerHTML = `<style data-emotion="emo ${hash}">.emo-${hash}{${css}}</style>`
+
+  const cache = createCache({ key: 'custom-key' })
+
+  expect(cache.inserted).toEqual({})
+  expect(document.documentElement).toMatchInlineSnapshot(`
+    <html>
+      <head />
+      <body>
+        <style
+          data-emotion="emo 1lrxbo5"
+        >
+          .emo-1lrxbo5{color:hotpink;}
+        </style>
+      </body>
+    </html>
+  `)
+
+  const cache2 = createCache({ key: 'emo' })
+
+  expect(cache2.inserted).toEqual({ [hash]: true })
+  expect(document.documentElement).toMatchInlineSnapshot(`
+    <html>
+      <head>
+        <style
+          data-emotion="emo 1lrxbo5"
+        >
+          .emo-1lrxbo5{color:hotpink;}
+        </style>
+      </head>
+      <body />
+    </html>
+  `)
+})
+
+test('Existing client-side inserted styles from Emotion 10 should not be moved', () => {
+  // the nested nature isn't special, it's just meant to be a general "make sure they're not moved"
+  safeQuerySelector(
+    'body'
+  ).innerHTML = `<div><style data-emotion="css-global"></style><div><style data-emotion="css"></style></div></div>`
+  expect(document.documentElement).toMatchInlineSnapshot(`
+    <html>
+      <head />
+      <body>
+        <div>
+          <style
+            data-emotion="css-global"
+          />
+          <div>
+            <style
+              data-emotion="css"
+            />
+          </div>
+        </div>
+      </body>
+    </html>
+  `)
+
+  const css = `color:hotpink;`
+  const hash = hashString(css)
+  let thing = document.createElement('div')
+  thing.innerHTML = `<style data-emotion="css ${hash}">.css-${hash}{${css}}</style>`
+  safeQuerySelector('body').appendChild(thing)
+  jest.resetModules()
+  require('@emotion/react')
+
+  expect(document.documentElement).toMatchInlineSnapshot(`
+    <html>
+      <head>
+        <style
+          data-emotion="css 1lrxbo5"
+          data-s=""
+        >
+          .css-1lrxbo5{color:hotpink;}
+        </style>
+      </head>
+      <body>
+        <div>
+          <style
+            data-emotion="css-global"
+          />
+          <div>
+            <style
+              data-emotion="css"
+            />
+          </div>
+        </div>
+        <div />
+      </body>
+    </html>
+  `)
+})
diff --git a/packages/cache/src/index.js b/packages/cache/src/index.js
index 36946ee65..741cce9f0 100644
--- a/packages/cache/src/index.js
+++ b/packages/cache/src/index.js
@@ -56,9 +56,25 @@ let createCache = (options: Options): EmotionCache => {
     const ssrStyles = document.querySelectorAll(
       `style[data-emotion]:not([data-s])`
     )
+
     // get SSRed styles out of the way of React's hydration
-    // document.head is a safe place to move them to
+    // document.head is a safe place to move them to(though note document.head is not necessarily the last place they will be)
+    // note this very very intentionally targets all style elements regardless of the key to ensure
+    // that creating a cache works inside of render of a React component
     Array.prototype.forEach.call(ssrStyles, (node: HTMLStyleElement) => {
+      // we want to only move elements which have a space in the data-emotion attribute value
+      // because that indicates that it is an Emotion 11 server-side rendered style elements
+      // while we will already ignore Emotion 11 client-side inserted styles because of the :not([data-s]) part in the selector
+      // Emotion 10 client-side inserted styles did not have data-s (but importantly did not have a space in their data-emotion attributes)
+      // so checking for the space ensures that loading Emotion 11 after Emotion 10 has inserted some styles
+      // will not result in the Emotion 10 styles being destroyed
+      const dataEmotionAttribute = ((node.getAttribute(
+        'data-emotion'
+      ): any): string)
+      if (dataEmotionAttribute.indexOf(' ') === -1) {
+        return
+      }
+
       ;((document.head: any): HTMLHeadElement).appendChild(node)
       node.setAttribute('data-s', '')
     })
@@ -82,14 +98,13 @@ let createCache = (options: Options): EmotionCache => {
     container = options.container || ((document.head: any): HTMLHeadElement)
 
     Array.prototype.forEach.call(
-      document.querySelectorAll(`style[data-emotion]`),
+      // this means we will ignore elements which don't have a space in them which
+      // means that the style elements we're looking at are only Emotion 11 server-rendered style elements
+      document.querySelectorAll(`style[data-emotion^="${key} "]`),
       (node: HTMLStyleElement) => {
         const attrib = ((node.getAttribute(`data-emotion`): any): string).split(
           ' '
         )
-        if (attrib[0] !== key) {
-          return
-        }
         // $FlowFixMe
         for (let i = 1; i < attrib.length; i++) {
           inserted[attrib[i]] = true
