Transdermal patches (adhesive patches placed on the skin) may also be used to deliver a steady dose through the skin and into the bloodstream. Testosterone-containing creams and gels that are applied daily to the skin are also available, but absorption is inefficient (roughly 10%, varying between individuals) and these treatments tend to be more expensive. Individuals who are especially physically active and/or bathe often may not be good candidates, since the medication can be washed off and may take up to six hours to be fully absorbed. There is also the risk that an intimate partner or child may come in contact with the application site and inadvertently dose himself or herself; children and women are highly sensitive to testosterone and can suffer unintended masculinization and health effects, even from small doses. Injection is the most common method used by individuals administering AAS for non-medical purposes. 
If testosterone deficiency occurs during foetal development, then masculinisation of the foetus will fail to occur normally and this may give rise to disorders of sex development. If testosterone deficiency occurs during puberty, a boy’s growth may slow and no growth spurt will be seen. The child may also fail to develop full sexual characteristics (hypogonadism) associated with men undergoing puberty, including development of pubic hair, growth of the penis and testes and deepening of the voice. Around the time of puberty, boys with too little testosterone may also have less than normal strength and endurance, and their arms and legs may continue to grow out of proportion with the rest of their body.
Endogenous androgens, including testosterone and dihydrotestosterone (DHT), are responsible for the normal growth and development of the male sex organs and for maintenance of secondary sex characteristics. These effects include the growth and maturation of prostate , seminal vesicles, penis and scrotum; the development of male hair distribution, such as facial, pubic, chest and axillary hair; laryngeal enlargement, vocal chord thickening, alterations in body musculature and fat distribution. Testosterone and DHT are necessary for the normal development of secondary sex characteristics.