Experimental studies have shown prenatal testosterone injection produces male-typical changes in dermatoglyphics and in palmar digit length, but not in bone digit length. Moreover, this effect occurs in digit 2 but not in digit 4. Additionally, human epidermal tissues have only androgen receptors and no estrogen receptors-α. Thus, it is likely that dermatoglyphic tissues in fingers may be more sensitive to prenatal testosterone effect, whereas, as reported above, bone digit ratios may be sensitive to testosterone-to-estrogen ratio. Hence, the palmar 2D:4D ratio reflects a combination of two different hormonal sensitivities. In support of this, a 2019 study has shown that differential placing of flexion creases contributes to sex differences in the palmar 2D:4D ratio.