Large Language Models

When Personalization Misleads: Understanding and Mitigating Hallucinations in Personalized LLMs

ZZhongxiang SunYYi ZhanCChenglei ShenWWeijie YuXXiao ZhangMMing HeJJun Xu
Published
January 16, 2026
Authors
7
Word Count
9,298

Ensuring factual accuracy in personalized AI systems.

Abstract

Personalized large language models (LLMs) adapt model behavior to individual users to enhance user satisfaction, yet personalization can inadvertently distort factual reasoning. We show that when personalized LLMs face factual queries, there exists a phenomenon where the model generates answers aligned with a user's prior history rather than the objective truth, resulting in personalization-induced hallucinations that degrade factual reliability and may propagate incorrect beliefs, due to representational entanglement between personalization and factual representations. To address this issue, we propose Factuality-Preserving Personalized Steering (FPPS), a lightweight inference-time approach that mitigates personalization-induced factual distortions while preserving personalized behavior. We further introduce PFQABench, the first benchmark designed to jointly evaluate factual and personalized question answering under personalization. Experiments across multiple LLM backbones and personalization methods show that FPPS substantially improves factual accuracy while maintaining personalized performance.

Key Takeaways

  • 1

    Personalization in LLMs can distort factual information.

  • 2

    Factuality-Preserving Personalized Steering (FPPS) mitigates hallucinations.

  • 3

    FPPS targets specific layers to preserve factual accuracy.

Limitations

  • FPPS may not fully eliminate all personalization-induced distortions.

  • The method's effectiveness varies across different LLM architectures.

Keywords

personalized large language modelsfactual reasoningpersonalization-induced hallucinationsrepresentational entanglementFactuality-Preserving Personalized SteeringPFQABenchinference-time approachfactual accuracypersonalized performance

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