I'm sorry to hear that your skin becomes dull or looks darker after applying a product. This reaction could be due to several reasons, such as:

• Irritation or allergic reaction: Some ingredients in skincare products can cause irritation or sensitivity, leading to dullness or darkening.
• Photosensitivity: Certain products increase your skin's sensitivity to sunlight, which can cause darkening or uneven skin tone.
• Product ingredients: Some ingredients might not suit your skin type, causing buildup or clogging pores, resulting in a dull appearance.

To help address this:

• Stop using the product temporarily to see if your skin improves.
• Use gentle, fragrance-free skincare products.
• Always apply sunscreen during the day to protect your skin from UV damage.
• Consider patch testing new products before full application.

If the issue persists or worsens, I recommend consulting a dermatologist who can evaluate your skin and suggest appropriate treatments or alternatives tailored to your skin type.To narrow down potential causes, we will need some more information.Please tell me your age and gender.