diff --git a/dev-packages/node-integration-tests/suites/tracing/double-baggage-prevention/instrument.mjs b/dev-packages/node-integration-tests/suites/tracing/double-baggage-prevention/instrument.mjs
new file mode 100644
index 000000000000..71a5cf60daae
--- /dev/null
+++ b/dev-packages/node-integration-tests/suites/tracing/double-baggage-prevention/instrument.mjs
@@ -0,0 +1,10 @@
+import * as Sentry from '@sentry/node';
+import { loggingTransport } from '@sentry-internal/node-integration-tests';
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  release: '1.0',
+  tracesSampleRate: 1.0,
+  tracePropagationTargets: [/localhost/],
+  transport: loggingTransport,
+});
diff --git a/dev-packages/node-integration-tests/suites/tracing/double-baggage-prevention/scenario.mjs b/dev-packages/node-integration-tests/suites/tracing/double-baggage-prevention/scenario.mjs
new file mode 100644
index 000000000000..f293a2479efa
--- /dev/null
+++ b/dev-packages/node-integration-tests/suites/tracing/double-baggage-prevention/scenario.mjs
@@ -0,0 +1,95 @@
+import * as Sentry from '@sentry/node';
+import http from 'http';
+
+let capturedHeaders = {};
+const targetServer = http.createServer((req, res) => {
+  capturedHeaders = {
+    'sentry-trace': req.headers['sentry-trace'],
+    baggage: req.headers['baggage'],
+  };
+  res.writeHead(200);
+  res.end('ok');
+});
+
+targetServer.listen(0, async () => {
+  const targetPort = targetServer.address().port;
+  const targetUrl = `http://localhost:${targetPort}/target`;
+
+  try {
+    // Step 1: fetch with manual getTraceData() headers
+    capturedHeaders = {};
+    await fetch(targetUrl, { headers: { ...Sentry.getTraceData() } });
+    const fetchHeaders1 = { ...capturedHeaders };
+
+    // Step 2: fetch without manual headers
+    capturedHeaders = {};
+    await fetch(targetUrl);
+    const fetchHeaders2 = { ...capturedHeaders };
+
+    // Step 3: http.request with manual getTraceData() headers
+    capturedHeaders = {};
+    await new Promise((resolve, reject) => {
+      const traceData = Sentry.getTraceData();
+      const req = http.request(
+        {
+          hostname: 'localhost',
+          port: targetPort,
+          path: '/target',
+          method: 'GET',
+          headers: traceData,
+        },
+        res => {
+          res.on('data', () => { });
+          res.on('end', () => resolve());
+        },
+      );
+      req.on('error', reject);
+      req.end();
+    });
+    const httpHeaders = { ...capturedHeaders };
+
+    // Step 4: fetch with custom + manual sentry baggage
+    capturedHeaders = {};
+    const traceData = Sentry.getTraceData();
+    await fetch(targetUrl, {
+      headers: {
+        ...traceData,
+        baggage: `custom-key=value,${traceData.baggage}`,
+      },
+    });
+    const fetchHeaders4 = { ...capturedHeaders };
+
+    const results = {
+      test1: {
+        sentryTrace: fetchHeaders1['sentry-trace'],
+        baggage: fetchHeaders1.baggage,
+        hasDuplicateSentryTrace: fetchHeaders1['sentry-trace']?.includes(','),
+        sentryBaggageCount: (fetchHeaders1.baggage?.match(/sentry-/g) || []).length,
+      },
+      test2: {
+        sentryTrace: fetchHeaders2['sentry-trace'],
+        baggage: fetchHeaders2.baggage,
+        hasDuplicateSentryTrace: fetchHeaders2['sentry-trace']?.includes(','),
+        sentryBaggageCount: (fetchHeaders2.baggage?.match(/sentry-/g) || []).length,
+      },
+      test3: {
+        sentryTrace: httpHeaders['sentry-trace'],
+        baggage: httpHeaders.baggage,
+        hasDuplicateSentryTrace: httpHeaders['sentry-trace']?.includes(','),
+        sentryBaggageCount: (httpHeaders.baggage?.match(/sentry-/g) || []).length,
+      },
+      test4: {
+        sentryTrace: fetchHeaders4['sentry-trace'],
+        baggage: fetchHeaders4.baggage,
+        hasDuplicateSentryTrace: fetchHeaders4['sentry-trace']?.includes(','),
+        hasCustomBaggage: fetchHeaders4.baggage?.includes('custom-key=value'),
+        sentryBaggageCount: (fetchHeaders4.baggage?.match(/sentry-/g) || []).length,
+      },
+    };
+
+  } catch (error) {
+    throw error;
+  } finally {
+    targetServer.close();
+  }
+});
diff --git a/packages/node-core/src/utils/baggage.ts b/packages/node-core/src/utils/baggage.ts
index be8e62b9497b..3def81e237d1 100644
--- a/packages/node-core/src/utils/baggage.ts
+++ b/packages/node-core/src/utils/baggage.ts
@@ -1,4 +1,20 @@
-import { objectToBaggageHeader, parseBaggageHeader } from '@sentry/core';
+import { objectToBaggageHeader, parseBaggageHeader, SENTRY_BAGGAGE_KEY_PREFIX } from '@sentry/core';
+
+/**
+ * To check if a baggage header contains any Sentry baggage values.
+ *
+ * @param baggageHeader The baggage header to check
+ * @returns true if the baggage header contains any keys with the 'sentry-' prefix
+ */
+export function hasSentryBaggageValues(baggageHeader: string | string[] | undefined): boolean {
+  if (!baggageHeader) {
+    return false;
+  }
+
+  const baggageString = Array.isArray(baggageHeader) ? baggageHeader.join(',') : baggageHeader;
+
+  return baggageString.split(',').some(entry => entry.trim().startsWith(SENTRY_BAGGAGE_KEY_PREFIX));
+}
 
 /**
  * Merge two baggage headers into one, where the existing one takes precedence.
diff --git a/packages/node-core/src/utils/outgoingFetchRequest.ts b/packages/node-core/src/utils/outgoingFetchRequest.ts
index ce04a26db1e0..837a9466e520 100644
--- a/packages/node-core/src/utils/outgoingFetchRequest.ts
+++ b/packages/node-core/src/utils/outgoingFetchRequest.ts
@@ -9,7 +9,7 @@ import {
   shouldPropagateTraceForUrl,
 } from '@sentry/core';
 import type { UndiciRequest, UndiciResponse } from '../integrations/node-fetch/types';
-import { mergeBaggageHeaders } from './baggage';
+import { hasSentryBaggageValues, mergeBaggageHeaders } from './baggage';
 
 const SENTRY_TRACE_HEADER = 'sentry-trace';
 const SENTRY_BAGGAGE_HEADER = 'baggage';
@@ -64,11 +64,14 @@ export function addTracePropagationHeadersToFetchRequest(
     const existingBaggagePos = requestHeaders.findIndex(header => header === SENTRY_BAGGAGE_HEADER);
     if (baggage && existingBaggagePos === -1) {
       requestHeaders.push(SENTRY_BAGGAGE_HEADER, baggage);
-    } else if (baggage) {
+    } else if (baggage && existingBaggagePos !== -1) {
       const existingBaggage = requestHeaders[existingBaggagePos + 1];
-      const merged = mergeBaggageHeaders(existingBaggage, baggage);
-      if (merged) {
-        requestHeaders[existingBaggagePos + 1] = merged;
+      // if existing baggage already has Sentry values, just skip it
+      if (!hasSentryBaggageValues(existingBaggage)) {
+        const merged = mergeBaggageHeaders(existingBaggage, baggage);
+        if (merged) {
+          requestHeaders[existingBaggagePos + 1] = merged;
+        }
       }
     }
   } else {
@@ -85,10 +88,12 @@ export function addTracePropagationHeadersToFetchRequest(
     const existingBaggage = request.headers.match(BAGGAGE_HEADER_REGEX)?.[1];
     if (baggage && !existingBaggage) {
       request.headers += `${SENTRY_BAGGAGE_HEADER}: ${baggage}\r\n`;
-    } else if (baggage) {
-      const merged = mergeBaggageHeaders(existingBaggage, baggage);
-      if (merged) {
-        request.headers = request.headers.replace(BAGGAGE_HEADER_REGEX, `baggage: ${merged}\r\n`);
+    } else if (baggage && existingBaggage) {
+      if (!hasSentryBaggageValues(existingBaggage)) {
+        const merged = mergeBaggageHeaders(existingBaggage, baggage);
+        if (merged) {
+          request.headers = request.headers.replace(BAGGAGE_HEADER_REGEX, `baggage: ${merged}\r\n`);
+        }
       }
     }
   }
diff --git a/packages/node-core/src/utils/outgoingHttpRequest.ts b/packages/node-core/src/utils/outgoingHttpRequest.ts
index 5292018e31ef..960a00fae7d4 100644
--- a/packages/node-core/src/utils/outgoingHttpRequest.ts
+++ b/packages/node-core/src/utils/outgoingHttpRequest.ts
@@ -12,7 +12,7 @@ import {
 } from '@sentry/core';
 import type { ClientRequest, IncomingMessage, RequestOptions } from 'http';
 import { DEBUG_BUILD } from '../debug-build';
-import { mergeBaggageHeaders } from './baggage';
+import { hasSentryBaggageValues, mergeBaggageHeaders } from './baggage';
 
 const LOG_PREFIX = '@sentry/instrumentation-http';
 
@@ -92,18 +92,22 @@ export function addTracePropagationHeadersToOutgoingRequest(
   }
 
   if (baggage) {
-    const newBaggage = mergeBaggageHeaders(request.getHeader('baggage'), baggage);
-    if (newBaggage) {
-      try {
-        request.setHeader('baggage', newBaggage);
-        DEBUG_BUILD && debug.log(LOG_PREFIX, 'Added baggage header to outgoing request');
-      } catch (error) {
-        DEBUG_BUILD &&
-          debug.error(
-            LOG_PREFIX,
-            'Failed to add baggage header to outgoing request:',
-            isError(error) ? error.message : 'Unknown error',
-          );
+    const existingBaggage = request.getHeader('baggage');
+    // if existing baggage already has Sentry values, just skip it
+    if (!hasSentryBaggageValues(existingBaggage as string | string[] | undefined)) {
+      const newBaggage = mergeBaggageHeaders(existingBaggage, baggage);
+      if (newBaggage) {
+        try {
+          request.setHeader('baggage', newBaggage);
+          DEBUG_BUILD && debug.log(LOG_PREFIX, 'Added baggage header to outgoing request');
+        } catch (error) {
+          DEBUG_BUILD &&
+            debug.error(
+              LOG_PREFIX,
+              'Failed to add baggage header to outgoing request:',
+              isError(error) ? error.message : 'Unknown error',
+            );
+        }
       }
     }
   }
diff --git a/packages/node-core/test/utils/baggage.test.ts b/packages/node-core/test/utils/baggage.test.ts
new file mode 100644
index 000000000000..a9597d617dd8
--- /dev/null
+++ b/packages/node-core/test/utils/baggage.test.ts
@@ -0,0 +1,90 @@
+import { describe, expect, it } from 'vitest';
+import { hasSentryBaggageValues, mergeBaggageHeaders } from '../../src/utils/baggage';
+
+describe('hasSentryBaggageValues', () => {
+  it('returns true for baggage with sentry- prefix', () => {
+    const baggage = 'sentry-environment=production,sentry-public_key=abc123';
+    expect(hasSentryBaggageValues(baggage)).toBe(true);
+  });
+
+  it('returns true for baggage with mixed sentry and non-sentry values', () => {
+    const baggage = 'custom-key=value,sentry-trace_id=123,another-key=foo';
+    expect(hasSentryBaggageValues(baggage)).toBe(true);
+  });
+
+  it('returns false for baggage without sentry values', () => {
+    const baggage = 'custom-key=value,another-key=foo';
+    expect(hasSentryBaggageValues(baggage)).toBe(false);
+  });
+
+  it('returns false for empty baggage', () => {
+    expect(hasSentryBaggageValues('')).toBe(false);
+  });
+
+  it('returns false for undefined baggage', () => {
+    expect(hasSentryBaggageValues(undefined)).toBe(false);
+  });
+
+  it('handles array of baggage headers', () => {
+    const baggage = ['custom-key=value', 'sentry-environment=production'];
+    expect(hasSentryBaggageValues(baggage)).toBe(true);
+  });
+
+  it('returns false for array without sentry values', () => {
+    const baggage = ['custom-key=value', 'another-key=foo'];
+    expect(hasSentryBaggageValues(baggage)).toBe(false);
+  });
+
+  it('handles baggage with whitespace', () => {
+    const baggage = 'custom-key=value, sentry-environment=production , another-key=foo';
+    expect(hasSentryBaggageValues(baggage)).toBe(true);
+  });
+
+  it('handles single sentry entry', () => {
+    const baggage = 'sentry-trace_id=abc123';
+    expect(hasSentryBaggageValues(baggage)).toBe(true);
+  });
+
+  it('is case-sensitive (does not match Sentry- or SENTRY-)', () => {
+    const baggage = 'Sentry-environment=production,SENTRY-trace=123';
+    expect(hasSentryBaggageValues(baggage)).toBe(false);
+  });
+});
+
+describe('mergeBaggageHeaders', () => {
+  it('returns new baggage when existing is undefined', () => {
+    const result = mergeBaggageHeaders(undefined, 'sentry-environment=production');
+    expect(result).toBe('sentry-environment=production');
+  });
+
+  it('returns existing baggage when new baggage is invalid', () => {
+    const existing = 'custom-key=value';
+    const result = mergeBaggageHeaders(existing, '');
+    expect(result).toBe(existing);
+  });
+
+  it('merges non-conflicting baggage entries', () => {
+    const existing = 'custom-key=value';
+    const newBaggage = 'sentry-environment=production';
+    const result = mergeBaggageHeaders(existing, newBaggage);
+    expect(result).toContain('custom-key=value');
+    expect(result).toContain('sentry-environment=production');
+  });
+
+  it('preserves existing entries when keys conflict', () => {
+    const existing = 'sentry-environment=staging';
+    const newBaggage = 'sentry-environment=production';
+    const result = mergeBaggageHeaders(existing, newBaggage);
+    expect(result).toBe('sentry-environment=staging');
+  });
+
+  it('handles multiple entries with conflicts', () => {
+    const existing = 'custom-key=value1,sentry-environment=staging';
+    const newBaggage = 'sentry-environment=production,sentry-trace_id=123';
+    const result = mergeBaggageHeaders(existing, newBaggage);
+    expect(result).toContain('custom-key=value1');
+    expect(result).toContain('sentry-environment=staging');
+    expect(result).toContain('sentry-trace_id=123');
+    expect(result).not.toContain('sentry-environment=production');
+  });
+});