Does stress accelerate balding?

There is not a lot of great medical evidence to support the notion that stress directly impacts MPB.  However, it probably has a minor role and only in some men and women with the right genetic background. Of course, we don't understand yet what that genetic background is at present.

When one examines studies of identical twins, one sees that 92% actually still look identical (same level of hair loss) years and years down the road. If stress, diet, and environmental factors played a huge role, one would not expect this number to be so high.

But for some males and females, it is likely that stress accelerates balding to a minor degree. A study by Gatherwright in 2013 suggested that higher stress could lead to worsening hair loss in the crown in men.  For women, a 2012 study suggested that higher stress was correlated with worse hair loss in the frontal area and divorce and separation were correlated with worsening hair loss in the temples.

Conclusion

Stress probably accelerates the rate of progression of balding in some individuals who have the right genetic predisposition.   We know that stress can cause an increased amount of daily shedding and such shedding can accelerate follicular miniaturization. It makes sense that stress can accelerate the balding process in some individuals. However, it's not likely to be a consistent phenomenon amongst all individuals.  

Reference

The contribution of endogenous and exogenous factors to male alopecia: a study of identical twins.

Gatherwright J, et al. Plast Reconstr Surg. 2013.

The contribution of endogenous and exogenous factors to female alopecia: a study of identical twins.

Gatherwright J, et al. Plast Reconstr Surg. 2012.