The needle length you choose to use depends on the kind of results you are wishing to achieve. 1mm and below will help even out skin texture and hyperpigmentation, but won't be as effective for reducing scarring. This length is also perfect for those who wish to improve the efficacy of their serums as the ingredients will penetrate deeper into the skin. The deeper a product can get into your skin, the more effective it will be at targeting your skincare concerns. 1mm - 2.5mm is recommended for those wishing to improve the appearance of acne scarring, fine lines and stretch marks, as well as anti-aging concerns. Remember multiple treatments are required for improvement in the appearance of these issues, performed every 4 weeks. It's advisable you consult with your doctor prior to performing at home microneedling treatments and for any skincare concerns.