# Fine-Tuning a Small Vision Language Model Using Synthetic Data for Explaining Bacterial Skin Disease Images

## TL;DR

This paper explores using a small vision language model fine-tuned with synthetic data to explain bacterial skin disease images, achieving strong diagnostic performance.

## Contribution

The study introduces a novel method of fine-tuning a compact VLM using synthetic QA supervision for dermatology image analysis.

## Key findings

- QA-only supervision results in the best report-generation performance.
- The combined QA+caption strategy achieves the highest classification accuracy of 70.20%.
- Synthetic data effectively enhances compact VLMs for medical image understanding.

## Abstract

Background/Objectives: Vision language models (VLMs) show strong potential for medical image understanding, but their large scale often limits practical deployment. This study investigates whether a compact VLM can be effectively adapted for dermatology, with a focus on explaining bacterial skin disease images. Methods: We curate a dataset derived from PMC-OA using the BIOMEDICA dataset and construct PMC-derma-VQA-bacteria by pairing images with inherited figure captions and synthetically generated question–answer (QA) supervision produced by Google’s Gemini model. SmolVLM is fine-tuned under three supervision settings: QA-only, caption-only, and a combined QA+caption strategy. The models are evaluated on a held-out test set for both text-generation quality and diagnostic classification performance. Results: QA-only supervision yields the best report-generation performance, while the combined QA+caption setting achieves the highest classification accuracy (70.20%). Conclusions: Synthetic QA supervision can meaningfully enhance compact VLMs for medical image understanding and diagnostic support in dermatology.