What mattress to stay away from?

What mattress to stay away from depends on health, allergies, and quality concerns, but generally mattresses to avoid include very cheap low density memory foam or polyfoam mattresses that off-gas strong chemical smells with high VOCs, contain fiberglass fire barrier that can shed particles, have no certifications like CertiPUR US or OEKO TEX, and sag quickly. Also avoid mattresses with known allergens if you have latex allergy, avoid natural latex mattress if allergic to latex. Avoid used mattresses due to hygiene, bed bugs, and dust mites. Avoid mattresses that are too soft or too firm for your sleep position causing back pain. For people with chemical sensitivities, avoid mattresses with synthetic latex and chemical flame retardants, choose certified organic or natural. For durability, avoid mattresses with low coil count or thin comfort layers that sag within year. Also avoid mattresses that trap heat if you sleep hot, like traditional memory foam without cooling. So stay away from cheap uncertified foam with fiberglass, used mattresses, mattresses that don't match your firmness needs, and latex mattresses if you have latex allergy. Look for certifications like CertiPUR US, OEKO TEX, GOLS for organic latex, and good warranty.