A skin sensitization measuring reagent comprising, as a main measuring agent, an organic compound having at least one thiol group derived from an amino acid and at least one amino group derived from a side chain of an amino acid, the organic compound having an absorption spectrum in an ultraviolet, visible, or near-infrared region and having a molar absorption coefficient of 100 L/mol·cm or more and 500,000 L/mol·cm or less at a maximal absorption wavelength; wherein the organic compound is represented by the following formula: W-[(L 1 -Xaa-L 2) p -Z] q wherein W represents a q-valent group having an absorption spectrum in the ultraviolet, visible, or near-infrared region, L 1 and L 2 each independently represent a single bond or a linking group, Xaa represents an amino acid residue, provided that p × q Xaa moieties include at least one lysine residue and at least one cysteine residue, Z represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, wherein the alkyl group having 1 to 6 carbon atoms is optionally substituted with a substituent selected from the group consisting of a carboxyl group, an amino group, a hydroxy group, a guanidyl group, a pyridine ring, and an imidazole ring, p represents an integer of 1 to 5, q represents an integer of 1 to 3, provided that p and q are not simultaneously 1, if p is 2 or more, L 1 -Xaa-L 2 moieties may be the same or different, and if q is 2 or more, [(L 1 -Xaa-L 2) p -Z] moieties may be the same or different. wherein the organic compound is represented by the following formula: W-[(L 1 -Xaa-L 2) p -Z] q wherein W represents a q-valent group having an absorption spectrum in the ultraviolet, visible, or near-infrared region, L 1 and L 2 each independently represent a single bond or a linking group, Xaa represents an amino acid residue, provided that p × q Xaa moieties include at least one lysine residue and at least one cysteine residue, Z represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, wherein the alkyl group having 1 to 6 carbon atoms is optionally substituted with a substituent selected from the group consisting of a carboxyl group, an amino group, a hydroxy group, a guanidyl group, a pyridine ring, and an imidazole ring, p represents an integer of 1 to 5, q represents an integer of 1 to 3, provided that p and q are not simultaneously 1, if p is 2 or more, L 1 -Xaa-L 2 moieties may be the same or different, and if q is 2 or more, [(L 1 -Xaa-L 2) p -Z] moieties may be the same or different. W represents a q-valent group having an absorption spectrum in the ultraviolet, visible, or near-infrared region, L 1 and L 2 each independently represent a single bond or a linking group, Xaa represents an amino acid residue, provided that p × q Xaa moieties include at least one lysine residue and at least one cysteine residue, Z represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, wherein the alkyl group having 1 to 6 carbon atoms is optionally substituted with a substituent selected from the group consisting of a carboxyl group, an amino group, a hydroxy group, a guanidyl group, a pyridine ring, and an imidazole ring, p represents an integer of 1 to 5, q represents an integer of 1 to 3, provided that p and q are not simultaneously 1, if p is 2 or more, L 1 -Xaa-L 2 moieties may be the same or different, and if q is 2 or more, [(L 1 -Xaa-L 2) p -Z] moieties may be the same or different.