Mutagens can be classified into two broad categories :

Physical Mutagens : Radiations are the most important physical mutagens. These are of two types.

• Ionizing Radiations :  These include X-rays, gamma-rays, alpha-rays and beta-rays. These cause breaks in chromosomes and cells show abnormal cell division.
• Non-Ionizing Radiations : These include UV rays. They have longer wavelengths but lower energy, and thus are insufficient to induce ionization. Thymine dimer formation is the major effect.

Chemical Mutagens : Large numbers of chemical mutagens exists. These are more harmful. Usually divided into two groups

• Mutagenic to both replicating and non replicating DNA - Nitrous Acid
• Mutagenic to Replicating DNA - Acridine Dyes, Base Analogues