A therapeutic serum suitable for inclusion in a cosmetic preparation may be produced by stressing a co-culture including proliferative cells. The co-culture of cells may be obtained by first establishing a monolayer of cells on a surface. After a monolayer of first culture is established, a second culture comprising more resilient and/or aggressive cells may be over-seeded on the monolayer and established. Additional cultures comprising increasingly dominant cells may then be over-seeded and established until a monolayer having the desired population of cells is obtained. The monolayer is then stressed to obtain a serum by conditioning a collection medium. The obtained serum may be combined with a suitable cosmetic base to provide a cosmetic preparation.
