steroid hormone
A steroid hormone is a fat-based message carved from cholesterol. All steroids share the same four-ring carbon skeleton; small chemical tweaks to that scaffold turn the same raw material into cortisol, aldosterone, testosterone, estradiol, or progesterone. Because they are oily rather than watery, steroids behave very differently from peptide hormones at every stage.
Steroid-producing cells do not store their product in granules. Instead they synthesize it on demand through a chain of enzyme steps (steroidogenesis), so release is governed by how fast the cell can make the hormone. Once in the blood, a steroid's oily nature is a problem: it does not dissolve well in plasma, so most of it rides bound to carrier proteins, with only a small free fraction active at any moment.
Because steroids are lipophilic, they slip straight through the cell membrane and bind receptors inside the cell, often in the nucleus. There the hormone-receptor complex acts as a switch on DNA, turning genes on or off. This is why steroid effects are typically slower to start but longer-lasting than the rapid surface signaling of peptide hormones.
Under chronic stress the adrenal cortex steadily makes cortisol, a steroid hormone, because it cannot stockpile a pre-made supply.
Synthesis-on-demand is a defining feature of steroid hormones.
Unlike peptide hormones, steroids survive digestion and can often be given by mouth — prednisone and birth-control pills are everyday examples.