Dark circles can be caused by various factors, including lack of sleep, genetics, aging, and even certain skincare products. If you suspect that your lash serum is causing dark circles, here are a few steps you can take to address the issue:

1. Identify the culprit: Determine if the lash serum is indeed causing the dark circles. Stop using the serum for a few weeks and observe if the dark circles improve. If they do, it's likely that the serum is the cause.

2. Check the ingredients: Look for potential irritants or sensitizing ingredients in the lash serum. Common culprits include fragrance, preservatives like parabens, and certain oils. Discontinue use if any of these ingredients are present.

3. Focus on hydration: Dark circles can be exacerbated by dry skin. Ensure your skin is well-hydrated by using a moisturizer suitable for your skin type. Look for ingredients like hyaluronic acid, glycerin, and ceramides, which help retain moisture.

4. Use a gentle eye cream: Incorporate an eye cream specifically formulated to address dark circles into your skincare routine. Look for ingredients like vitamin C, niacinamide, caffeine, and peptides, which can help brighten the under-eye area and improve circulation.

5. Get enough sleep: Lack of sleep can contribute to the appearance of dark circles. Aim for 7-9 hours of quality sleep each night to promote overall skin health.

6. Protect your under-eye area: Apply sunscreen with at least SPF 30 to protect the delicate skin around your eyes from further damage caused by UV rays.

If the dark circles persist or worsen, it's best to consult a dermatologist or skincare professional for a personalized assessment and treatment plan. They can help determine the underlying cause and provide appropriate recommendations.