There could be several reasons why your lash serum may not be working as expected. Here are a few possibilities to consider:

1. Inadequate or inconsistent use: Lash serums usually require consistent and regular application to see results. If you are not using the serum as instructed or if you are skipping applications, it may affect the effectiveness of the product.

2. Insufficient active ingredients: Check the ingredient list of your lash serum. Look for key active ingredients such as peptides, vitamins, or plant extracts that are known to promote lash growth. If the serum lacks these essential ingredients or if they are present in low concentrations, it may not deliver the desired results.

3. Product quality: Not all lash serums in the market are created equal. Some products may be of lower quality or may not contain the ingredients they claim to have. It's important to research and choose a reputable brand that has positive customer reviews and a proven track record.

4. Individual differences: Results can vary from person to person due to individual variations in lash growth cycles, genetics, and overall health. Some individuals may naturally have slower lash growth or less noticeable results compared to others.

5. Underlying health conditions: Certain medical conditions or medications can affect lash growth. If you have any underlying health issues or are taking medications that may impact hair growth, it's worth consulting with a healthcare professional to rule out any potential factors that may be hindering the effectiveness of the lash serum.

Remember, it's important to be patient when using lash serums, as it can take several weeks to see noticeable improvements. If you have tried using the serum consistently for an extended period of time and still see no results, it may be worth exploring alternative options or consulting with a dermatologist or trichologist for further guidance.