In order to understand the answer, it is necessary to clarify what is the internal environment of the body. The body of any vertebrate organism, including humans, is topologically a cylindrically closed plane of a certain thickness, with processes - limbs, at one end of which there is a mouth, and at the other - an anus. Actually, the internal environment of the body is the thickness of this plane, and even the limbs. Everything that is outside and inside the cylinder is the external environment of the body. Exactly; even what you put in your mouth and swallow is, nevertheless, outside of you. Or, if you want, you surround your dinner with yourself. The same applies to the air you breathe - in the nose, trachea, and lungs - the air is outside of you, since the respiratory tract is the external environment of the body.
Smelling occurs when the molecules of some substances end up on the membrane of the olfactory receptor located in the upper part of the nasal cavity. A certain combination of nerve impulses then enters the olfactory center of the brain and is perceived as a smell. Thus, we can assume that the molecules of odorous substances do not penetrate further the surface of the body. Although, of course, with a sufficient concentration of certain substances in the air, they begin to be absorbed in the lungs into the bloodstream and end up inside the body.
The sensory nerve endings of the olfactory neurons end in the layer of the mucous secretion of the nasal cavity, the excitation of their signal occurs when odor-carrying molecules enter this secret. If by particles of a substance we mean molecules, then, of course, one way or another we inhale them. If larger, then not necessarily. Only relatively small molecules enter the bloodstream through the respiratory tract. But when swallowed, even larger molecules can be resorbed.
Perhaps, in normal living conditions, this or that concentration of a substance will enter the bloodstream. The smell of a substance is not always identical, a person does not have a very rich set of olfactory expressed genes (about 1000). But the set of molecules is not very specific. If you smell the perfume, it is not the fragrance itself that is absorbed, but, more likely, other components. Likewise, the macromolecules of the cat's wool will not be absorbed, and therefore, in case of allergies, they will cause hay fever, and not anaphylactic shock. But the smaller components will probably get there. The question is whether they are odorless. You need to know at least approximately the molecular weight of the substance.
Not always. When a substance enters the olfactory receptor, this substance dissolves in the secret and stimulates the production of an impulse that enters the olfactory center. But thanks to the protective properties of the nasal cavity, these particles are washed off and removed. But if these are aggressive particles (acids, alkalis), then yes, some part enters the bloodstream, that is, into the body.