What type of hormones can pass through the cell membrane?

Steroid hormones are unique among the hormone types because of their hydrophobic nature, which allows them to easily pass through the lipid bilayer of cell membranes. Steroid hormones are derived from cholesterol and include hormones such as testosterone, estrogen, and cortisol. Since cell membranes are primarily composed of phospholipid layers, which repel water-soluble substances, the non-polar structure of steroid hormones enables them to diffuse directly across the membrane.

Once inside the cell, steroid hormones bind to specific intracellular receptors, thereby influencing gene expression and cellular function. This mechanism of action is different from that of peptide hormones, amino acid derivatives, and protein hormones, which are typically hydrophilic or polarized and cannot pass through the cell membrane without the aid of specific receptors on the cell surface. Instead, they exert their effects by binding to receptors on the cell membrane, leading to second messenger signaling pathways inside the cell.