1. Non-porous materials: Non-porous materials, such as silicone, stainless steel, and glass, are safer to use because they do not harbor bacteria and are easier to clean.

2. Porous materials: Porous materials, such as jelly rubber and cyberskin, are less safe to use because they can harbor bacteria and are harder to clean. They may also contain potentially harmful chemicals.

3. Phthalates: Phthalates are chemicals that are often added to plastic products to make them more flexible. They have been linked to health issues such as cancer and reproductive problems. It's best to avoid dildos that contain phthalates.

4. Size and shape: Consider the size and shape of the dildo to ensure that it is comfortable and enjoyable to use.

5. Brand reputation: Look for a reputable brand that is known for producing high-quality sex toys. Reading reviews from other customers can also be helpful.

I hope this information is helpful! If you have any other questions, don't hesitate to ask.